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Copyright 2010 ERDAS, Inc. All Rights Reserved.Printed in the
United States of America.
cc02/06 Part No. 1873
The information contained in this document is the exclusive
property of ERDAS, Inc. This work is protected under United States
copyright law and other international copyright treaties and
conventions, to include the Berne and Geneva Phonograms
Conventions, the WIPO Copyright Treaty, and the World Trade
Organization.
No part of this work may be reproduced or transmitted in any
form or by any means, electronic or mechanical, including
photocopying and recording, or by any information storage or
retrieval system, except as expressly permitted in writing by
ERDAS, Inc. All requests should be sent to the attention of Manager
of Customer Education at the following address:
ERDAS, Inc.5051 Peachtree Corners CircleNorcross, Georgia
30092-2500 USA
Phone: 770 / 776-3400Fax: 770 / 776-3694
Support Services: 800 / 953-6643Customer Education: 800 /
373-2713Web: www.erdas.com
The information contained in this document is subject to change
without notice.
Warning
All information in this document, as well as the software to
which it pertains, is proprietary material of ERDAS, Inc., and is
subject to a ERDAS license and non-disclosure agreement. Neither
the software nor the documentation may be reproduced in any manner,
without the prior written permission of ERDAS. Specifications are
subject to change without notice.
About This Manual
This Introduction to LPS exercise manual is an instructional
document designed to be a part of the Intermediate level courses
offered by ERDAS Educa-tion Services. At the Intermediate level,
the courses offered consist of the IMAGINE VirtualGIS, Using
Imagery to Update Your GIS, Cartography with Map Composer, and the
Introduction to the LPS course. All ERDAS education courses provide
corresponding instructional documentation.
Trademarks
ERDAS IMAGINE, IMAGINE Essentials, IMAGINE Advantage, IMAGINE
Professional, IMAGINE GLT, TopoMouse, and Stereo Analyst are
registered trademarks of ERDAS. LPS, IMAGINE VirtualGIS, and
CellArray are trademarks of ERDAS. Geospatial Imaging Chain is a
service mark of ERDAS, Inc. Other brands and product names are
trademarks of their respective owners.
Acknowledgments
The QuickBird imagery and associated data provided in this
Photogrammetry Course and Exercise Manual are courtesy of
DigitalGlobe, Longmont, CO. Any use or distribution of this data by
others, or outside the realm of ERDAS Education Services, is
strictly prohibited.
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iv Introduction to LPS
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ERDAS Customer Education Introduction to LPS 1
Table of ContentsTable of Contents
.........................................................................1
Using This Manual
.........................................................................3
Section 1: Creating a BlockExercise 1: Raw Scanned Imagery
.................................................... 11
Challenge 1: Scale Variation
.......................................................... 19
Exercise 2: LPS Setup Wizard
......................................................... 25
Exercise 3: Imagery Requirements
................................................... 35
Exercise 4: Inside the
Sensor..........................................................
41
Exercise 5: The Sensor in Space
...................................................... 51
Exercise 6: Take Control
...............................................................
55
Exercise 7: Building the Relationship
................................................ 83
Exercise 8: The Triangulation Results
............................................... 91
Section 2: DTM ExtractionExercise 1: In Search of
Z..............................................................
97
Exercise 2: Visualizing Your DEM
....................................................109
Exercise 3: Statistical DTM
Evaluation..............................................113
Exercise 4: Verifying Results
.........................................................117
Section 3: Creating and Working with Ortho ImagesExercise 1:
Orthorectification
.......................................................125
Exercise 2: Working with DigitalGlobe Data
.......................................129
Exercise 3: Mosaic Images
............................................................147
Exercise 4: Visualizing Your Images
.................................................153
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2 Introduction to LPS Table of Contents
Section 4: LPS Terrain EditorExercise 1:
Introduction...............................................................161
Exercise 2: DTM Editing Tools
........................................................177
Exercise 3: Setting a Constant Elevation
...........................................189
AppendixAppendix A - Geometric Models in LPS
.............................................197
Appendix B - Terrain Editor Operators
.............................................201
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ERDAS Customer Education Introduction to LPS 3
Using This Manual
Introduction
This manual contains step-by-step instructions on how to perform
certain processes. You should be aware that each exercise provides
a single path through ERDAS IMAGINE and LPS tools. In most cases,
there are various ways to maximize tool usage, depending on the
individual project.
This exercise manual is provided to the student, along with all
images and copies of the presentation slides used by the
instructor. This provides the capability for recreating the
processes performed in class at a later date, as well as the key
points on any theory involved.
Exercise Conventions
Section Title Page
States the objective of the exercises and lists the application
tools to be utilized within the various tasks.
Exercise Tasks Each exercise is split into a set of tasks. After
the course, these tasks will help you locate within the manual
where you performed a certain set of steps.
Questions These appear in a larger font with both bold and
italic attributes. The instructor may quiz and/or review with you,
following each exercise.
Class Notes These pages follow the end of each exercise on which
notes from your studies can be made.
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4 Introduction to LPS Using This Manual
Notational Conventions
Bold Italicized Text
Any text, which is bold, indicates a filename, or parameter to
be changed or selected.
Graphics To help you locate icons and objects used in the
exercises, the icons will be next to the icon name in the text.
Insets These italicized captions will appear in the outside
margin of the page. They define terms or explain theory behind the
steps you are being asked to perform.
Diagrams These are an optional means to direct you in the usage
of some of the applica-tions tools.
The following graphics are also used for particular
purposes:
This is a note or a quick tip. It gives additional relevant
infor-mation, or describes other ways of using the software.
This is information relating to the application of the current
tools.
This is a reference. It provides additional theory or science
that will help in using the tools.
This is a warning. It cautions you regarding potential pitfalls
and how to avoid producing errors.
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ERDAS Customer Education Introduction to LPS 5
Mouse and Keyboard Conventions
LMB Left mouse button
MMB Middle mouse button
RMB Right mouse button
LMB + Shift Hold down the Shift key plus left mouse button
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6 Introduction to LPS Using This Manual
Windows Terminology
Title bar
Open file button
Radio button (enabled)
Radio button (disabled)
Text box with nudgers
Popup list
Checkbox (enabled)
Button (enabled)
Button (disabled)
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ERDAS Customer Education Introduction to LPS 7
The eWorkspace
ERDAS Application Menu button
QuickAccessToolbar Title bar
Active Layer type
Hiddenpanel
Dockedpanel
Ribbon
2D View Status BarMap View
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8 Introduction to LPS Using This Manual
The Ribbon Explained
Group
CollapsedGroup
ExpandedGroup
Unselected tab
Properties button
Selected tab
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ERDAS Customer Education Introduction to LPS 9
Section 1: Creating a Block
Section Objective
Students will use the ERDAS IMAGINE Viewer to study scanned
images as well as examine the inherent errors in raw imagery. This
will help explain the need for orthorectification.
Subsequent exercises will guide you through the process of
setting up LPS, entering information about the sensor used, and
adding control points.
Finally, the section will explain the triangulation process and
how to evaluate the results of the process.
Tools Used
Viewer Used to visualize imagery, zooming, inquiring and
measuring features.
LPS Set Up Wizard
Set up the basics parameters associated with a block.
Point Measurement Tool
Used to digitize and measure control and tie points on your
imagery.
Triangulation Report
View the statistics and residuals of a triangulation to evaluate
accuracy and help locate errors.
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10 Introduction to LPS Section 1: Creating a Block
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ERDAS Customer Education Introduction to LPS 11
Exercise 1: Raw Scanned Imagery
Objective: To become familiar with the dataset and review the
eWorkspace.
Task 1: Setting Session Prefer-ences
1. Start ERDAS IMAGINE.
The ERDAS IMAGINE eWorkspace opens.
1
3
5
6
7
8
4
2
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12 Introduction to LPS Section 1: Creating a Block
2. From the eWorkspace, click the ERDAS Application button .
From the menu, select Open > Raster Layer. The Select Layer to
Add dialog displays. This dialog is used throughout ERDAS
IMAGINE.
3. From the ERDAS IMAGINE Main Menu select Session |
Prefer-ences. The Preference Editor displays.
1) ERDAS Application Menu button
Access to New, Open, Save, View, Print, Session, Batch,
Configuration, Preferences and Help.
2) Quick Access Menu One-click access to commonly used
functions. Customizable.
3) Ribbon Access to IMAGINE functions, collected in tabs and
groups
4) Title bar Window Title, Window (Viewer) display icons:
Minimize, Maximize, Close
5) 2D View Main Viewing space. Can add multiple views, Map View,
3D View.
6) Contents Pane Display and arrange all layers each View.
7) Shoebox Organizes easily-accessed shortcuts to your data.
8) Status Bar Cursor identification and image coordinates
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ERDAS Customer Education Introduction to LPS 13
4. From the Category list, ensure that User Interface &
Session is selected. This displays the default preferences that are
associated with the data location and data properties.
5. As the Default Data Directory, type the path to where the
course data is located. (Your instructor will provide this
information.)
6. As the Default Output Directory, type the path to where all
outputs generated in this course will be saved. (Your instructor
will provide this information.)
7. In the Category list, select Viewer, and the preferences for
the Viewer display.
8. Scroll down (vertical scroll bar on the right side) to the
Clear Display, Fit to Frame, and Background Transparent
options.
By default, the Clear Display option is enabled and the Fit to
Frame and Back-ground Transparent options are disabled.
9. Enable the Fit to Frame and Background Transparent checkboxes
and disable the Clear Display checkbox to set these as new defaults
for the Raster Options dialog.
10. Click User Save and Close.
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14 Introduction to LPS Section 1: Creating a Block
Task 2: Display a Raw Scanned Aerial Photo
In this exercise we will be using the eWorkspace to view an
image.
1. From the eWorkspace, click the ERDAS Application button .
From the menu, select Open > Raster Layer. The Select Layer to
Add dialog displays.
2. In the Select Layer to Add, navigate to the LPS directory,
and ensure the Files of type is set to IMAGINE Image (*.img), then
select the file: 11_189.img
3. Before clicking Ok, click the Raster Options tab, ensure that
the Fit to Frame checkbox is enabled, and for the Layers to Colors,
set Red to 1, Green to 2 and Blue to 3, then click OK.
4. In the Attention dialog, disable the Always Ask checkbox and
click Yes.
Task 3: Locating and Identifying Fea-tures
In the next steps, you will identify a location on the image
using the Inquire Cursor.
1. Right Mouse Button (RMB) click on the image and from the
Quick View menu, select Inquire Cursor. This will start the Inquire
Cursor and display the Inquire Cursor dialog.
2. Move the Inquire Cursor onto the image.
We are calculating Pyramid Layers to facilitate quick view-ing
within IMAGINE. LPS pyramid layers are more complex than IMAGINE
pyramid layers, so we will ahve to recalcu-late them again
later.
You may also select the Inquire Cursor by clicking on its
icon from the Viewer toolbar.
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ERDAS Customer Education Introduction to LPS 15
3. In the Inquire Cursor dialog, click the pull-down arrow for
Coordi-nate Type and select File.
What are the units of measurement the Coordinate Type-File is
using?
Where on the image is the origin of the file coordinate
type?
4. Input the following X and Y coordinates, then press
Enter:
While viewing a feature, there are a number of tools that let
you zoom in and out. The tools used in this exercise are the
Interactive Zoom In and the Interactive Zoom Out.
5. Click the Interactive Zoom In icon .
6. Hold down the Left Mouse Button (LMB) and drag the mouse to
place a box around the feature identified above. When you release
the mouse button, the view will zoom in.
7. To move around the image, click the Roam Image icon , then
LMB click and hold to drag the image.
X = 3579.80 Y= 2634.30
The pointer displays as a magnifying glass as you posi-tion it
on the image.
The Interactive Zoom In icon can be used to zoom in 2 times by
left clicking on the image.
The Interactive Zoom Out icon can be used to zoom out 2 times by
clicking on the image.
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16 Introduction to LPS Section 1: Creating a Block
8. Take a minute to practice roaming around the image, looking
at differ-ent features found in Denver.
9. Click Close in the Inquire Cursor dialog.
10. Close the Viewer without saving changes.
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ERDAS Customer Education Introduction to LPS 17
Class Notes
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18 Introduction to LPS Section 1: Creating a Block
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ERDAS Customer Education Introduction to LPS 19
Challenge 1: Scale Variation
Objective: To identify inconsistencies with are inherent in raw
scanned imagery
Task 1: Scale Calculation Using Raw Imag-ery
On these raw images, it is difficult to see any scale variation.
To help us check for scale variations throughout the raw image, we
will compare measurements at two different photo locations.
Ground distances collected from other sources will be used to
help us determine photo scales.
Scale Variation: occurs in all photogra-phy, due to objects
being closer to or fur-ther away from the camera. The scale is not
constant across a photo.
The first distance you will measure is the length of the field
at the coordinates listed previously.
1. In the eWorkspace, click the Open Layer icon on the Quick
Access toolbar.
2. In the Select Layer to Add, navigate to the LPS directory,
and ensure the Files of type is set to IMAGINE Image (*.img), then
select the file: 11_189.img. The image may take a minute to
load.
3. Use the Zoom and Roam tools so that you can see the length of
the field in your Viewer.
4. From the Home tab, Information group, click the Measure icon
.
The Measurement Tool displays.
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20 Introduction to LPS Section 1: Creating a Block
5. Leave the Measurement Units set to the default (Other), which
rep-resents pixels.
6. Use the Zoom tools to zoom into the bottom left end of the
field.
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ERDAS Customer Education Introduction to LPS 21
7. From the Measurement Tool dialog, click the Measure Lengths
and Angles icon .
8. Place the cursor over this point and click to take the
beginning mea-surement. You should now see a line extending from
this point to your cursor.
9. Roam to the other end of the field by moving your cursor
outside the Viewer. Continue roaming until you reach the identified
location in the images, then place the cursor over that point and
double-click to take your end measurement.
10. Make a note of the distance displayed: ______________
pixels
11. Use the following equation to calculate the distance in
centimeters:
__________ pixels / 400 = __________ centimeters
12. Then note your results:
Football field length is ______________ centimeters
To scroll through the image horizontally, use Shift +
Scroll-wheel.
To scroll vertically through the image, use Ctrl +
Scroll-wheel.
To change pixel measurements into centimeters, we must know the
scanning resolution. These images were scanned at 25 microns,
meaning that each pixel is 25 microns across. 10,000 microns equals
1 centimeter. Therefore, there are 400 pixels in a centimeter.
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22 Introduction to LPS Section 1: Creating a Block
13. Click Zoom to Data Extent .
14. Open the Inquire Cursor and navigate to following
coordinates:
X= 5493 Y= - 6943
15. Zoom in on the pitchers mound on which the Inquire Cursor is
placed.
16. From the Measurement Tool dialog, click the Measure Lengths
and Angles icon .
The distance you will be measuring is defined by a line in the
image following. The line extends from the baseball pitchers mound
to the football 50 yard line.
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ERDAS Customer Education Introduction to LPS 23
17. Place the cursor over the pitchers mound and click to take
the begin-ning measurement.
18. RMB click in the Viewer. This temporarily turns off the
measure-ment that you are taking.
19. In the Inquire Cursor dialog, input the following
coordinates:
X= 3576 Y= - 2677
20. Move the cursor back into the Viewer and the measurement
will be on again. Double-click on the 50 yard line of the football
field.
What is the length you measured? ______________ centimeters
From these raw photo distances, the photo scale can be
determined. Listed below are the ground distances for the above
features.
What are some sources where we can get ground distances?
21. Calculate the photo scale using the following equation:
Photo scale = (ground distance * 100) / photo distance
22. Record the scale for each of the measured distances:
What causes the scale variations?
If there were no changes, what would this mean in reference to
the orientation of the airplane and the ground?
23. Close all open Viewers and tools without saving changes.
Football Field 91.44 meters
Pitcher's mound to 50 yard line 2608.10 meters
Football Field 1: __________
Pitcher's mound to 50 yard line 1: __________
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24 Introduction to LPS Section 1: Creating a Block
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ERDAS Customer Education Introduction to LPS 25
Exercise 2: LPS Setup Wizard
Objective: To open a new LPS project and input the setup
parameters required by the Block Properties Setup tool.
You will begin your work with a Setup Wizard that guides you
through the process of defining the project. The linear workflow
helps to quickly select your camera or sensor model, the
projection, spheroid and datum, and the units.
Task 1: Defin-ing a Project
1. From the Toolbox tab, click the LPS icon . This will launch
LPS without a project loaded.
2. From the LPS menu, select File | New. The Create New Block
File dialog displays.
3. Navigate to the Outputs directory and type denver_frame.blk
as the File name. Click OK.
Alternatively, you can click the Create new block file icon
.
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26 Introduction to LPS Section 1: Creating a Block
Task 2: Choosing a Camera Model and Map Projection
1. From the Model Setup dialog, select Frame Camera, then click
OK. The Block Property Setup box displays. From this, a reference
sys-tem must be set. In a production environment it may take time
to research the reference system.
This dialog is used to select the model for use with your block
file images. The model defines the geometric proper-ties associated
with the sensor or camera.
All Geometric Models are listed and described in Appendix A.
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ERDAS Customer Education Introduction to LPS 27
2. Click the Set button. The Projection Chooser dialog
displays.
A few parameters must be set in order to define the Map
Projection.
3. Display denver-5m-dem.img in a Viewer.
4. To obtain the projection, select the Home tab and then click
the Layer
Info button . The ImageInfo dialog displays.
5. Click the Projection tab.
The Projection Chooser handles the selection of LPS's standard
projections, or creates a custom projection.
During this exercise a custom projection will be created, and
saved as a standard projection.
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28 Introduction to LPS Section 1: Creating a Block
6. Fill in the following information:
7. In the ImageInfo dialog, select File | Close, then close the
Viewer.
8. In the Projection Chooser dialog, click the Custom tab, and
in the appropriate fields, input the parameters collected above,
then click Save.
Is the data North or South of the equator?
9. For the new Projection Name, type Denver and for the In
Category, select UTM WGS 84 North, then click OK.
What are some circumstances, which require you to create more
than one block for use in the same project?
Projection _______________
Spheroid ________________
Datum ___________________
Zone Number _____________
North or South ____________
It is important to enter the units correctly. Once the block has
been created there is no going back to change the units. A new
block would have to be created and valuable time may be lost.
The information does not have to be typed into the boxes. You
may choose the appropriate information from the pull-down
menus.
By saving Denver to the Standard projection tab, the new
projection can be used at a later date.
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ERDAS Customer Education Introduction to LPS 29
10. Click the Standard tab, and in the UTM WGS 84 North
category, select Denver as your projection, then click OK. The
projection infor-mation displays in the Block Property Setup.
11. Click the Next button.
12. For this exercise, set the Angle Units to Degrees.
Task 3: Setting Frame-Specific Information
The Rotation System and the Photo Direction must be set. Each
image or photo is defined in its relation to the ground, by 3
rotation angles (omega, phi, kappa).
In the most common rotation system, Omega is the primary axis.
The primary axis is the axis about which the first rotation occurs.
Positive rotations occur clockwise around the axes, as you look in
a positive direction along the axis (e.g., looking from 0 to
X).
In the Denver data, around which axes are the following
rotations? (Use On-Line Help as a reference)
These photos of Denver use the Omega, Phi, Kappa Rota-tion
System (Position and orientation of the sensor as it existed when
the image or photo was captured).
Omega = ___________ axis
Phi = ___________ axis
Kappa = ___________ axis
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30 Introduction to LPS Section 1: Creating a Block
Which parts of the world use the following Rotation Systems?
13. We will leave the Photo Direction as the default, Z-axis for
normal images.
For what type of photography would you set the Photo Direction
to the Y-axis?
14. Using the following equation, calculate the flying height,
then input the result into the appropriate box in the Block
Properties Setup.
Phi(+), Omega, Kappa __________________
Phi(-), Omega, Kappa ___________________
The Photo Direction must also be set. The Photo Direction equals
the Optical Axis of the Camera. The Optical Axis is a straight line
extending from the perspective center, through the center of the
lens to the ground. The perspective center is the point in space
where the image was exposed.
The Import Exterior Orientation Parameters button allows for the
import of existing exterior orientation data, that are provided by
photogrammetric systems, such as analytical stereo plotters,
digital photogrammetric workstations, or post-processed airborne
GPS data recorded at the time of image capture.
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ERDAS Customer Education Introduction to LPS 31
Flying Height (fh) = Focal Length (f) x Scale (h) / 1000
15. Click OK to close the Block Property Setup dialog, which
automati-cally opens the LPS dialog.
16. From the LPS menu, select File | Save. It is good practice
to save your block before continuing.
What are some of the parameters set during the Block setup?
17. After the Block has been saved, select File | Close.
The block you have just created is based on a Frame Camera
Geometric Model. The block can be reopened at a later time.
Task 4: SPOT Push-broom Geometric Model
For this next task, you will be creating another block but this
time, it will be based on a SPOT Pushbroom model.
1. Click the Create new block file icon .
2. From the dialog that displays, click the Goto button, and
navigate to the Outputs directory.
3. For the block File name, type denver_spot, then press
Enter.
Polynomial-based Pushbroom: A sen-sor type which scans an area
along parallel lines, perpendicular to the direction of
move-ment.
4. Click OK and the Model Setup dialog displays. From the
dialog, select Polynomial-based Pushbroom from the Geometric Model
Category.
5. As the Geometric Model, select SPOT Pushbroom, then click
OK.
6. Click Set. The Projection Chooser dialog displays.
The photography for Denver was taken with a 153.475 mm focal
length camera and the photo scale in approximately 1:21,000.
Make sure all your parameters have been entered correctly before
you click OK. Once acknowledged, the block is defined and only the
flying height can later be altered (Edit | Block Properties |
Model-Specific). If changes thereafter, are necessary, a new block
will have to be defined.
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32 Introduction to LPS Section 1: Creating a Block
7. From the Standard tab, select the Denver projection you
created previously, then click OK.
8. Once the projection reference has been set, ensure that
Meters has been selected as the Horizontal Units.
What is the major difference you have noted between setting up a
Frame Camera and a Spot Geometric Model?
9. In the Block Properties Setup, click OK. The block is created
and the project is now listed in the LPS Project Manager.
10. To save the block, select File | Save, then from the LPS
Block Tool, select File | Close.
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ERDAS Customer Education Introduction to LPS 33
Class Notes
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34 Introduction to LPS Section 1: Creating a Block
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ERDAS Customer Education Introduction to LPS 35
Exercise 3: Imagery Requirements
Objective: Review the imagery formats, which can be imported
into LPS, and generate pyra-mid layers.
Our block has been setup and defined, the main LPS dialog
displays, and the task now, is to bring in the imagery. Before
processing, we must understand the imag-ery requirements and
limitations.
Task 1: Import Files into the Block
The LPS Project Manager window is displayed but does not have a
project loaded.
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36 Introduction to LPS Section 1: Creating a Block
1. Click the Open block file icon . The Block File Name dialog
dis-plays
2. Click the Recent button and select denver_frame.blk, and then
click OK.
3. In the Block File Name dialog, click OK.
4. From the LPS icon panel, click the Add Frame to the List icon
. The Image File Name dialog displays.
Dynamic Loadable Library (DLL): Allows non-native LPS files to
be read directly by the application.
5. Use the Files of Type pull-down menu to look at the file
types avail-able for loading into LPS.
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ERDAS Customer Education Introduction to LPS 37
The list displays file formats, which use a DLL when being
loaded for viewing by LPS.
6. From the Image File Name dialog, select 11_188.img,
11_189.img, and 11_190.img. Click OK.
7. Update the Description column by giving 11_188.img the name
denver1. Give 11_189.img the name denver2 and 11_190.img the name
denver3.
8. Take a look at the column headings and the contents of the
columns.
When inputting images, you have the option of inputting one
image at a time, or a number of images.
This is accomplished by selecting one image at a time or by
highlighting the first image, holding the SHIFT key and clicking on
the last image to add, then clicking OK to load the data.
If you are unable to see the full Description, place the mouse
cursor to the right of the word Description. The cur-sor changes to
a dual-ended arrow.
Pyramid Layers
Interior Orientation
Exterior Orientation
Digital Terrain Model
Orthorectified
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38 Introduction to LPS Section 1: Creating a Block
What do the 'X's in the active column mean, and what processes
are associated with this column? (Hint: Use On-Line Help.)
In what situation would the Online column be colored red?
Task 2: Creating Pyramid Layers
Pyramid layers are copies of the original layer(s) that have
been successively reduced by a power of 2, and then resampled. The
number of pyramid layers cre-ated will depend on the size of the
image. A large image will produce more pyra-mid layers.
Pyramid layers are added as additional layers in the .img file.
However, these lay-ers cannot be accessed for display.
1. Click on any red-colored cell in the Pyr. column. The Compute
Pyra-mid Layers dialog displays, from which you have the following
three options:
One Image Selected
All Selected Images
All Images Without Pyramids
2. Maintain the default of All Images Without Pyramids, then
click OK. The cells in the pyramid layers should turn green.
The green color patches in the matrix cells indicate that the
feature has been created, or that the process has been run and
completed. Red indicates the step still needs to be completed.
This visual guide can help you determine which steps have been
performed for each of the images in your Block File.
This will take some time depending on the number of images in
the list.
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ERDAS Customer Education Introduction to LPS 39
What are the differences between ERDAS IMAGINEs pyramid layers
and LPS's pyramid layers?
3. In the LPS dialog, select File | Save to save your image
list.
We have imported our imagery into an LPS block and created
pyramid layers. We must now give LPS the sensor information, and
setup the camera, as well as the image parameters.
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40 Introduction to LPS Section 1: Creating a Block
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ERDAS Customer Education Introduction to LPS 41
Exercise 4: Inside the Sensor
Objective: Perform Interior Orientation by entering camera
parameters and measuring the Fiducial Marks.
Task 1: Defin-ing the Sensor
At this point, the pyramid layers have been created for the
images to be used; the green color patch in the Pyr. column is a
visual indication of this.
1. From the LPS menu, select Edit | Frame Editor, or click the
Show
and Edit Frame Properties icon .
The Frame Editor dialog displays with the information for the
currently selected image (i.e., the image with the caret symbol
next to it).
2. To ensure the image you selected is the correct one, click on
the View Image button. A Viewer displays your image.
3. Once you have confirmed it is the correct image, close the
open Viewer.
The Next and Previous buttons can be used to scroll through all
of your images and change parameters, without having to return to
the main Block Tool dialog.
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42 Introduction to LPS Section 1: Creating a Block
ISCS: Many aspects of aerial cameras are accurately measured in
a laboratory. These measurements should be provided to you as a
report.
4. Click the New Camera button and the Camera Information dialog
dis-plays. In this case, the Camera Name refers to the aerial
camera type.
5. In the Camera Information dialog, click the Load button,
locate and select (highlight) the denver_frame.cam file, then click
OK.
6. Review the information from the camera file, such as:
Photogrammetry is essentially the process of establishing a
relationship between the camera/sensor, the imagery, and the
ground.
To build this mathematical relationship, we must be able to
define points on the images, points on the ground, and the location
of the sensor.
To define the points on the images, we need to setup an
Image-Space Coordinate System (ISCS).
To do this we need information about the camera/sensor
itself.
Focal Length
Principal Point xo
Principal Point yo
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ERDAS Customer Education Introduction to LPS 43
Fiducials Marks: marks within the cam-era body which are
transferred to the film during exposure. The locations of these
marks are measured in a laboratory and then placed into the
calibra-tion report.
7. Fiducial marks can be located and displayed in the imagery.
Click the Fiducials tab.
If you needed to change the Number of Fiducials you could make
that change under this tab.
Where on the image are the fiducials located?
8. Click the Radial Lens Distortion tab.
Are the Distortion Coefficients editable?
9. Click OK. The camera information for the first image has been
entered.
10. Click Next to ensure that denver_frame is being used as the
Sensor Name for image 11_189.img, then repeat for the final
image.
Task 2: Fiducial Orientation and Measuring Fiducials
LPS assumes the same camera collected all of the images, so you
do not need to input this information for each image. However, if
the camera did change, we could use the Next or Previous buttons to
navigate to the desired image, and modify the camera and fiducial
information.
1. In the Frame Editor dialog, click the Interior Orientation
tab. The Film X and Y positions, which were entered by the camera
file, are displayed.
What values do the Image X and Image Y columns contain and why
are they initially empty?
Lenses are never perfect. The Radial Lens Distortion parameter
will model any errors found in the lens by the lab-oratory
technician. These errors can then be taken into account during
processing.
Although not a requirement, we can add the radial lens
distortion to help further define the camera. In this exam-ple, we
will not be using any Lens Distortion Parameters.
If the Field Angles and Distortion are entered into the
CellArray, the Calculate Coeffs button would be clicked. The three
Konrad Distortion Coefficients would then be cal-culated. These are
used to mathematically model the distor-tion in the lens.
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44 Introduction to LPS Section 1: Creating a Block
You will select the correct Fiducial Orientation. To determine
the correct orienta-tion, typically, you would locate the data
strip. The Y-axis should lie parallel to this strip. In the
airphotos provided, the data strip has been removed. Your
instructor will indicate to you the orientation of the
fiducials.
2. For this exercise, select the fourth icon . This icon best
portrays our images orientation.
3. Now, use the Next and Previous buttons to set the Fiducial
Orienta-tion for the other two images. Then use the Previous button
to return to the first image.
During scanning, how important is it to keep the scan
orientation constant?
4. Under the View Fiducial Locator heading, click the Open
Viewer icon . A Main View opens on top of the Frame Editor
dialog.
5. To prevent an unwanted measurement from being taken, click
the Select Image Fiducial icon .
Once the camera parameters have been entered, the fiducial marks
must be measured. Their measured pixel location (c,r) is compared
to their calibrated coordinates (mm). This allows the position of
the principal point of each image to be calculated, which then
becomes the origin of the image coordinate system.
The pixel coordinates and the calibrated coordinates are used to
calculate transformation coefficients. Any pixel coordinate can
then be transformed into image coordinates.
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ERDAS Customer Education Introduction to LPS 45
A Main View, an Over View, and a Detail View display. You will
use these views to measure the fiducials.
6. Take a minute to select each of the Fiducial Orientation
buttons and note the location, (i.e. which corner), of the Link
Cursor in the Over View. When finished, return to the correct
orientation.
Any of the three views can be used for measuring the fidu-cials;
however, it is advisable to measure in the Detail View.
Before measuring the fiducials, verify the positioning of the
Link Cursor, as different Fiducial Orientation buttons are
selected.
The Link Cursor in the Main View identifies the approximate area
of the fiducial. This area is magnified in the Detail View.
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46 Introduction to LPS Section 1: Creating a Block
7. Click and drag in the center of the Link Cursor in the Main
View, and move it over the top of the first fiducial mark.
What effect does this change have on the Detail View?
Some fiducial centers may be difficult to see. Adjustments may
be made using the brightness and contrast sliding bar.
8. Place the cursor over the Detail View, RMB click, and select
Set Res-ampling Method. The default resampling method Nearest
Neighbor displays in the Set Resampling Method dialog.
9. Click OK. The image becomes pixelated.
10. RMB click on the Detail View, select Set Resampling Method
then use the pull-down menu to choose Bilinear Interpolation.
11. Repeat this process but for the Resampling Method, choose
Cubic Convolution.
Which resampling method best displays the fiducial center?
Once you can accurately identify the center of the fiducial, you
are ready to take a measurement.
12. Click the Place Image Fiducial icon . This changes your
cursor into a crosshair when placed over any one of the
Viewers.
13. Take your first measurement by clicking over the fiducial
center in the Detail View.
14. Repeat the previous steps to measure the second fiducial
mark.
15. When these first two fiducials have been measured, click the
Auto Locate button. The Automatic Interior Orientation window
displays, which will be used to locate the remaining fiducial
marks.
16. Click the Current Frame radio button, and then click
Run.
The fiducial point is measured in Image pixel coordinates, and
the Frame Editor CellArray is automatically updated. The display
automatically updates and moves to the next fiducial since the Set
Automatic Move icon is enabled.
If the Set Automatic Center icon is enabled, then the fiducial
that you digitize will snap to the fiducial center if it is within
two pixels.
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ERDAS Customer Education Introduction to LPS 47
17. When finished, click Accept then Close.
What could cause a higher than expected RMS error?
What is a good RMSE?
18. Click in the row for the Point # you wish to view. Click the
Select Image icon if you need to reposition the mark.
19. When you are satisfied with the fiducial measurements in the
first image, click the Auto Locate button again, then click the
Unsolved Frames radio button.
20. Click Run, and when complete, click Accept then click Close,
and inspect the fiducial measurements for the last two frames, just
as you did the first.
Your Root Mean Square Error (RMSE), in pixels and microns, is
displayed above the Solve button on the Interior Orientation tab of
the Frame Editor.
RMSE - After each measurement, each fiducial's file coordi-nates
(r,c pixels) are transformed into image coordinates (millimeters).
These new coordinates are then retrans-formed back into file
coordinates (r,c pixels).
The variation (residual) between the initial file coordinates
and the retransformed coordinates, are indications of the
closeness-of-fit of the two coordinate sets.
Any RMSE values larger than 0.5 pixels, or ones which are half
the scanning resolution of the image, infer systematic and/or
measurement errors. Check for film deformation, poor scanning
quality, mis-measured points, and incorrect calibration.
Based on your RMSE, you may want to re-measure some of the
fiducials. Frequently, the first few measurements are not as
accurate as the latter measurements.
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48 Introduction to LPS Section 1: Creating a Block
21. Once you have finished, click OK in the Frame Camera Frame
Editor dialog.
You will notice that the Int. column has turned green;
indicating that you are fin-ished defining the interior orientation
of the camera.
22. From the LPS Project Manager menu, select File | Save, or
click the Save Block Information icon .
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ERDAS Customer Education Introduction to LPS 49
Class Notes
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50 Introduction to LPS Section 1: Creating a Block
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ERDAS Customer Education Introduction to LPS 51
Exercise 5: The Sensor in Space
Objective: To input the position and orientation of the sensor
(Exterior Orientation).
Task 1: Examine Parameters for Exterior Orienta-tion
You should have your LPS Project Manager open, and it should
contain three images, each of which now has the Int. column as
green.
1. Open the Frame Editor and click the Exterior Information tab.
You will see six columns.
The first three columns define the perspective center
coordinates, while the next three represent the rotational angles
of this perspective center, and hence, the image.
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52 Introduction to LPS Section 1: Creating a Block
2. Confirm that the Status row is Unknown for all six
elements.
3. LPS will compute:
Can we get the Perspective Center coordinates from the
images?
Exterior orientation defines the position and orientation
associated with an image.
To build the relationship between Image and Object space, the
software needs to determine the rotational differences between the
two coordinate systems.
Xo, Yo, and Zo define the location of the perspective
center.
Phi (), Omega (), and Kappa () define the rotation of this
perspective center.
As part of its calculations Leica Photogrammetry Suite can
determine these six (6) values for each image.
The Std. (standard deviation) row represents the reliability you
place on the Values. The lower the Std. the more reli-able your
coordinate information.
Initial: This status indicates the exterior orientation value is
an approximation to the actual value, and will be modified during
triangulation.
Fixed: The value will not be modified during triangulation.
Unknown: This status assumes you have no information about the
camera's exterior orientation parameters.
Omega () - a rotation around the ______ axisPhi () - a rotation
around the __________ axisKappa () - a rotation around the _______
axis
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ERDAS Customer Education Introduction to LPS 53
4. Click OK in the Frame Editor.
We are now ready to input control points that form the basis of
the mathematical calculations used to tie the image to the
ground.
5. In the Project Manager, click the Save icon .
Be aware that measurements and parameters input are not saved
into the Block by clicking OK.
Once the exterior parameters are input, LPS uses these values to
establish the positional and rotational relationship between the
image space coordinate system and the ground space coordinate
system.
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54 Introduction to LPS Section 1: Creating a Block
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ERDAS Customer Education Introduction to LPS 55
Exercise 6: Take Control
Objective: You will become familiar with some of the tools used
to input and collect ground control points (GCPs). After measuring
the fiducials of each image in your block, you are ready to measure
the position of points on the ground.
Task 1: The Point Measure-ment Tool
1. From the LPS menu, click the Point Measurement icon .
2. Ensure that the Classic Point Measurement Tool radio button
is selected.
3. Click OK. The Point Measurement dialog displays, which is
divided into sections as labeled on the following page.
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56 Introduction to LPS Section 1: Creating a Block
In the Right View and the Left View of the Point Measurement
dialog, there are options to change or specify the image
displayed.
To build the relationship between the ground and images, we need
to share some values measured in each space coordinate system
(Object & Image).
For the ground or object space, we measure GCPs using a
coordinate system (X,Y,Z). These same points are then measured on
the images (x,y). These two sets of numbers are then used to start
to build this relationship.
Point Measurement Group
Left View Group Right View Group Tools Group
Over View Detail View Detail View Over View
Main View Main View
CommonTools
Left ViewTools
Right View Tools
Reference Sources
Reference (Ground) Coordinates File (Image) Coordinates
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ERDAS Customer Education Introduction to LPS 57
4. Ensure that image 11_188 is in the Left View and image 11_189
is in the Right View.
5. Adjust the brightness, then click Apply and review the
modifications in the Viewer.
6. Click the Reset button to return the image to its original
appearance.
If you had a large block of images, you would use these menus to
'scroll' through the images as you measure the GCPs.
Each image has its own brightness and contrast tools. This tool
can be useful when viewing, identifying, and measuring GCPs.
At the bottom of the Point Measurement dialog, there are two
CellArrays. Both are empty until points are input. The Reference
CellArray (left), is where ground coordinates for each point are
displayed.
Type Usage
Full - Control or check points with X, Y, and Z coordinates.
Control - Points used as control points during triangulation.
(X, Y, Z are known.)
Horizontal - Points with X and Y coordinates. The Z coordinate
is unknown and can be estimated during triangulation.
Check - Points are used to inde-pendently verify the quality of
a tri-angulation. (X, Y, Z are known.)
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58 Introduction to LPS Section 1: Creating a Block
The File CellArray, which is on the right, is where pixel
coordinates are displayed. These coordinates are generated when you
digitize the position of your Reference (Ground Control)
points.
From what sources could we obtain reference coordinates?
What units are used in the File CellArray?
Vertical - Points with Z coordi-nates. The X and Y coordinates
are unknown and can be estimated or ignored during
triangulation.
Tie - Points appearing in the over-lapping areas of two or more
images. (The X, Y, Z coordinates are unknown and determined dur-ing
triangulation.)
None - Tie points with X, Y, and Z coordinates that are
estimated dur-ing triangulation.
X Reference, Y Reference, Z Reference - Ground coordinates of
each point.
Image Name - Name of the image where the ground control
measurement was taken.
Active - X indicates that this measurement will be used in the
aerial triangulation.
X File, Y File - Pixel coordinates (row and col-umn) of the
measurement.
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ERDAS Customer Education Introduction to LPS 59
Task 2: Importing GCP Coordinates from an ASCII File
1. From the ERDAS menu , select View > View Text Files to
open
the Text Editor.
2. Use the Open File icon and navigate to the LPS directory.
3. Select the denver_gcp.txt file, and click OK. The GCP ASCII
file dis-plays.
4. Make note of the number of GCPs, then select File | Close in
the Text Editor.
5. In the Common Tools section of the Point Measurement dialog,
click the Import Points icon .
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60 Introduction to LPS Section 1: Creating a Block
6. In the Import/Export Points dialog, click OK.
7. In the Reference ASCII File dialog, select denver_gcp.txt and
click OK.
8. In the Reference Import Parameters dialog, click OK.
9. If an Attention dialog appears, click Yes.
10. In the Import Options dialog, click the View button. This
will open the file in the Text Editor. Leave this Text Editor
open.
11. From the text file, decide which is the appropriate
Separator Character.
12. In the Import Options dialog, ensure that the Separator
Character is set to WhiteSpace and that the Row Terminator
Character is set to NewLine(Unix).
When would we need to edit the Field column?
13. Once the changes have been made, click OK in the Import
Options. The selected columns in the Reference CellArray will
populate.
14. Select File | Close in the Text Editor. The GCPs we input
have X, Y, Z coordinates and will be used as control points.
In the Import Options dialog, listed under Column Mapping, are
the selected columns from the Reference CellArray. Input Field
Number is the denver_gcp.txt column number to be imported into the
Reference CellArray.
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ERDAS Customer Education Introduction to LPS 61
What does the 'X' in the Active column mean? (Use On-Line
Help)
Now that we have the ground coordinates of these points, you
will measure them on the images.
15. Click the Viewing Properties icon .
16. In the Viewing Properties dialog, enable the Advanced radio
button, and then enable the Residual checkbox. Click OK.
17. Click the Set Automatic (x,y) Drive icon . Following the
second measured GCP, the position will automatically move to the
next point.
A second way to import Reference points:
Click the Horizontal Reference icon .
From the GCP Reference Source dialog, enable the ASCII File (3D)
radio button.
In the Reference ASCII File dialog, navigate to the LPS
directory.
Select denver_gcp.txt and click OK.
In the Reference Import Parameters, click OK.
In the Import Options dialog, click OK.
The Point ID values would then need to be imported.
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62 Introduction to LPS Section 1: Creating a Block
18. In the Reference (Ground) Coordinates section of the Point
Mea-surement dialog, place the caret next to the first reference
point.
19. Ensure that the Left View is set to 11_188.
20. In the overview for image 11_188, click and drag the cursor
box to the first GCP location (visual aids to find the GCPs are
provided at the end of this task for reference).
21. Use the Main View and Detail View windows to fine-tune the
position-ing. If the location is difficult to see, adjust the
contrast and/or bright-ness, and then click Apply to affect the
image.
22. Click Reset to set both the contrast and brightness back to
their origi-nal values.
23. Once you have located the point, click the Create Point icon
, move the cursor to the point in the Detail View window.
24. Click to take a measurement. After the measurement is taken,
a sym-bol and ID will display. Notice that the Image Name, along
with X and Y File coordinates appear in the CellArray on the
right.
25. Place the caret next to the second reference point. Use the
previ-ous procedure to digitize the remaining GCP locations,
generated from the ASCII file. When the GCP occurs in multiple
images, digitize the point in the additional image(s).
26. When the points have all been measured, click the Save
button.
If the caret is not moved to the first reference point, then the
first measured GCP will be correlated to the incorrect refer-ence
point and will need to be deleted and re-measured.
If the GCP needs to be moved, click to select the point then
drag it to the correct location.
Remember to move the caret (>) to each point before
digi-tizing.
Some GCPs will appear in all three images; you will need to use
the Right View and Left View pull-down menus to view all the
images.
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ERDAS Customer Education Introduction to LPS 63
X and Y Image Coordinates for the Ground Control Points
Point IDX File
11_188Y File
11_188X File
11_189Y File
11_189X File
11_190Y File
11_190
1 7300.869 1040.875 NA NA NA NA
2 7902.375 7432.905 NA NA NA NA
3 5876.865 5736.365 NA NA NA NA
4 3390.862 5161.596 6745.885 5107.455 NA NA
5 137.612 5240.366 3581.503 5119.324 6855.289 5224.150
6 NA NA 857.773 6577.114 4172.309 6653.906
7 NA NA 47.344 730.768 3558.664 885.625
8 NA NA NA NA 542.678 4238.856
9 NA NA NA NA 2358.746 7714.545
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64 Introduction to LPS Section 1: Creating a Block
GCP Locations
GCP #1
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ERDAS Customer Education Introduction to LPS 65
GCP #2
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66 Introduction to LPS Section 1: Creating a Block
GCP #3
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ERDAS Customer Education Introduction to LPS 67
GCP #4
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68 Introduction to LPS Section 1: Creating a Block
GCP #5
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ERDAS Customer Education Introduction to LPS 69
GCP #6
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70 Introduction to LPS Section 1: Creating a Block
GCP #7
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ERDAS Customer Education Introduction to LPS 71
GCP #8
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72 Introduction to LPS Section 1: Creating a Block
GCP #9
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ERDAS Customer Education Introduction to LPS 73
Task 3: Adding a Reference image
All GCPs collected up to this point have been obtained from GPS
coordinates. The next point you will collect will be from a
reference image.
1. Click the Reset Horizontal Reference icon .
2. Ensure the Image Layer radio button is selected and click
OK.
3. In the Reference Image Layer dialog, select park.img and
click OK.
Under the Right View section, you will see that the Horizontal
reference has been set to park.img. This image is a subset of an
orthorectified IKONOS image. The area covered by this image can be
found in all three input images.
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74 Introduction to LPS Section 1: Creating a Block
4. From the Left View section, enable the Use Viewer As
Reference checkbox.
The Left View has been changed to park. In the next few steps,
you will obtain a GCP from the Reference image and then find that
point in all of the input images. Currently, the input images are
rotated at a 900 clockwise angle from park.img. In order to aid the
locating of a common point, park.img will be rotated to match the
input images.
5. RMB click in the Main View of park.img and select Rotate.
6. In the Rotate Image dialog, set the Rotation Angle to 90,
enable the Clockwise radio button, and click the ApplyToLeft
button.
7. Click Close.
8. Change the Right View to 11_188.
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ERDAS Customer Education Introduction to LPS 75
9. Click the Add button to add a tenth reference point.
10. Change the Type to Horizontal and the Usage to Control.
On the following page you will find the point to be
digitized.
11. Click the Create Point icon and measure the GCP in the
refer-ence image and in all of the input images.
12. When the point has been measured, click the Save button and
then disable the Use Viewer As Reference checkbox.
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76 Introduction to LPS Section 1: Creating a Block
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ERDAS Customer Education Introduction to LPS 77
Task 4: Adding Tie Points
Within the overlap between 2 or more images, you might be able
to identify the same ground feature on different images. You do not
need to know the coordi-nates (X,Y,Z) of this point. The Tie point
is used during triangulation and X, Y, Z coordinates are generated
for the Tie point when the triangulation is accepted.
You will use the same tools to add a Tie point to your set of
reference points.
1. Using the Link Box, locate a feature in the two viewable
images. Try and find a recognizable feature in both images using
the image below as a guide.
2. From the Common Tools section, click the Add button again,
then click the Create Point icon .
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78 Introduction to LPS Section 1: Creating a Block
3. To keep this tool active, click the Keep Current Tool icon
.
4. In the Detail View, place the cursor over the feature you
identified and digitize the point. Immediately, move the cursor to
the same fea-ture in the other image, and digitize again.
5. Repeat the above steps to digitize the Tie Point in the third
image.
6. Click the Automatic Tie Properties icon and make sure that
the following parameters are set:
7. Click OK in the Automatic Tie Point Generation Properties
dialog.
The Type (None) and Usage (Tie) will default to the correct
settings.
Tie points are very useful in the triangulation process, but
they can be very time-consuming to collect. Leica Photo-grammetry
Suite will automatically generate tie points. It uses a variation
of Feature-Based Matching.
Auto Tie Point Collection - involves image matching as a means
to identify ground features in overlapping areas of imagery. The
various matching methods can be divided into three categories
including:
Area based matching - Similarity of the gray level values within
correlation windows based over the imagery.
Feature based matching - Point features are extracted and
identified on adjacent images. The feature pair is given a
correlation value. Points with correlation values, which are closer
to 1, are recognized as better matches.
Relation based matching - Uses image features and the
relationship between the features. Time-consuming but very
accurate.
Images Used: All Available
Initial Type: Tie Points
Strategy Parameters: Avoid Shadow
Intended number of Points / Image:
25
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ERDAS Customer Education Introduction to LPS 79
8. Click the Perform Automatic Tie Generation icon . Tie Points
will be generated on each of the images.
The diagram below shows the configuration required to perform
automatic collec-tion on six overlapping images.
9. Click Close in the Auto Tie Summary dialog.
How many Tie points were generated?
Minimum Input Requirements for Automatic Tie Point Col-lection
for a Frame Camera, digital camera, videography, or non-metric
camera:
Initial approximations of ext.orientation (X, Y, Z, omega, phi,
kappa), OR
At least two GCPs per stereo pair, OR
At least two (2) Tie Points per stereo pair
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80 Introduction to LPS Section 1: Creating a Block
10. Visually inspect a sample of the collected tie points for
accurate placement. If you find that the Tie Points are slightly
off from the cor-rect position, adjust them.
11. Click the Select points common to both views icon . This
will highlight all points that are found in the images currently
displayed.
12. After all adjustments are completed, Save your
measurements.
We have completed the ground point measurements. We are now
ready to move on to the actual triangulation process, where a
relationship is mathematically built between your coordinates.
If the Tie Points do not match, and there are gross errors, ask
your instructor for assistance.
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ERDAS Customer Education Introduction to LPS 81
Class Notes
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82 Introduction to LPS Section 1: Creating a Block
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ERDAS Customer Education Introduction to LPS 83
Exercise 7: Building the Relationship
Objective: To perform aerial triangulation in LPS, using fewer
control points.
Task 1: Setup and Run Aerial Triangulation
You have now completed the ground point measurement and
generated tie points. The block file is now ready to have the
triangulation parameters set.
1. Ensure that the Point Measurement dialog is open, and the
Refer-ence and File coordinates are visible.
2. Click the Triangulation Properties icon . The Aerial
Triangula-tion dialog displays.
LPS uses a mathematical technique, known as Block Bun-dle
Adjustment, for aerial triangulation. Block bundle adjust-ment
performs three functions:
Determines the position and orienta-tion of each image at time
of exposure
Determines coordinates for the tie points in overlapping
areas
Identifies, removes, minimizes and distributes errors associated
with the imagery, GCPs etc.
There should be Xs in the Active column beside all Control and
Tie points. If there are not, click in the Active cells which do
not have X's.
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84 Introduction to LPS Section 1: Creating a Block
General Options
Maximum Iterations: Used in processing the aerial
triangu-lation.
Convergence Value: The limit for the correction of ground
coordinates in each iteration.
Point Options
Used to set the standard deviations (error estimates)
asso-ciated with the image and ground coordinates.
Image Point Standard Deviation (pixels): During the
triangu-lation process the image coordinate positions are allowed
to fluctuate within the limits of these values. Larger values
indicate poor image measurements.
Interior Options
Used to set the standard deviations for the interior
orienta-tion parameters (millimeters).
Fixed for all Images: Self-calibration will not take place
(i.e., the original focal length and principle point are
maintained).
Exterior Options
Used to set the standard deviations for the exterior
orienta-tion parameters, in meters and degrees.
Advanced Options
Additional Parameters Model: Used in the aerial triangula-tion
for the compensation of systematic image errors.
Use Image Observations of Check Points in Triangulation: Can
improve the precision of the solution.
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ERDAS Customer Education Introduction to LPS 85
3. In the General tab, leave the Maximum Iterations at 10 and
the Convergence Value as 0.001.
How is the Convergence Value derived? (Use On-line Help.)
4. Click the Advanced Options tab and ensure that the Use Image
Observations of Check Points in Triangulation checkbox is
dis-abled.
5. Click Run to proceed with the triangulation process. When
complete, a Triangulation Summary displays.
What is your Total Image Unit Weight RMSE?
During the triangulation process what is happening to the tie
point reference coordinates?
6. Record the RMSE values in the space below. You will be
comparing these values as you run through this exercise.
This form of Triangulation (Bundle Block Adjustment) uti-lizes
an iterative least squares solution. The iterations will continue
until the Maximum Iterations have been reached or the Convergence
Value is less than 0.001.
As the iterations continue, the original coordinates are
re-evaluated. If every difference between the re-evaluated and
original values is less than the convergence value, the itera-tions
will stop.
Total Image Unit-Weight RMSE: ______________
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86 Introduction to LPS Section 1: Creating a Block
Following are two examples of Triangulation Summaries. Both
RMSEs are expressed in pixels.
7. Look at the differences: While one has a good RMSE, the other
has a poorer RMSE; however, both reached convergence.
8. Click the Review button.
This records the overall accuracy of each measured point.
Control Point RMSE: ________________________
________________________
________________________
________________________
________________________
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ERDAS Customer Education Introduction to LPS 87
9. Make a note of the points with a high Total RMSE (for both
Ground Points and Image Points):
We will look at these in greater detail in the next
exercise.
10. Close the Review Triangulation Results dialog.
11. Click Close in the Triangulation Summary dialog.
12. Click OK in the Aerial Triangulation dialog.
Task 2: Changing Triangulation Parameters
1. In the Point Measurement dialog, disable all of the Tie
points and render them inactive by:
Highlight only the GCPs (i.e. Usage is set to Control) on the
list by clicking the Point # with the Shift + LMB
RMB click on the highlighted Point # and select Invert
Selection
Click on the Active column heading
RMB click over the Active column heading and select For-mula
Input a value of 0 in the Formula window and click Apply and
Close
You will now see all of the selected rows, which are highlighted
in yellow, become inactive.
2. Click the Perform Triangulation icon to re-run the aerial
trian-gulation.
How have the triangulation results been modified?
3. Close the Triangulation Summary.
4. In the Point Measurement dialog, replace the 'X's beside the
Tie points, making them active in the triangulation process. Use
the pro-cess given above and add a 1 into the Formula text box.
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88 Introduction to LPS Section 1: Creating a Block
5. Open the Triangulation Properties dialog and select the Point
tab, then set the GCP Type to Same Weighted Values. This will allow
the triangulation process to vary the GCP locations.
6. In the Aerial Triangulation dialog, click Run.
7. Close the Triangulation Summary, then click Cancel in the
Aerial Triangulation dialog.
We have looked at the triangulation process, and some of the
parameters that can be changed to improve the output results. We
have not yet considered the possi-bility of poor GCPs.
The next exercise will examine the triangulation results in more
detail, and search for poor GCP values.
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ERDAS Customer Education Introduction to LPS 89
Class Notes
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90 Introduction to LPS Section 1: Creating a Block
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ERDAS Customer Education Introduction to LPS 91
Exercise 8: The Triangulation Results
Objective: Study the Triangulation Report results and make
adjustments to improve the trian-gulation results.
Task 1: Analyze the Triangula-tion Report
The aerial triangulation report lists all of the input and
output values used during the triangulation process. The report can
be divided into several categories, but for a standard block the
most significant are probably:
1. Click the Report of Triangulation Results icon . The
Triangula-tion Report displays in the Text Editor.
2. In the Text Editor, select Find | Find, and in the edit box,
type itera-tion, then click Find.
How many iterations did it take to reach the convergence
value?
3. Look at the Standard Error for the last iteration. This value
is impor-tant since it accumulates the effect of each image
coordinate residual, to provide a global indicator of quality.
Control Point residuals
Check Point residuals
Image Coordinate results
By analyzing the Triangulation Report and finding the points
with the most error (relatively large residuals) you can start to
improve your triangulation.
Make note of the Output Units, mentioned at the top of the
report.
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92 Introduction to LPS Section 1: Creating a Block
What is the Standard Error following the last iteration and what
are its units?
4. In the Search and Replace dialog, input rX in the top, then
click Find.
5. Below, list the Point ID of the GCP with the largest
residuals:
Point ID rX rY rZ
6. This point may fall on more than one image. To see residuals
for each measurement, move to the residuals of image points section
at the bottom of the Text Editor. Look for the Point ID listed
above.
What Image were the poor residuals recorded on?
In what units are the residuals of image points?
7. Click Close in the Search and Replace dialog.
8. Select File | Close in the Text Editor.
Task 2: Removing GCPs and Re-run-ning the Triangula-tion
1. In the Reference CellArray of the Point Measurement dialog,
click on the 'X' in the Active column for the row with the GCP
mentioned above.
This point becomes inactive, and is no longer used in the
triangulation.
During the triangulation process GCP values (X,Y,Z) are
recalculated during each iteration. The newly calculated GCP
coordinates are compared to the original reference GCP coordinates,
and the differences (residuals) are listed.
This should take you to the portion of the report which
con-tains the residuals of the control points.
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ERDAS Customer Education Introduction to LPS 93
2. Click the Triangulation icon . The Triangulation Summary
dis-plays.
What is the new Total Image Unit-Weight RMSE?
3. Click the Report button. Use the scroll bar to move down
through the triangulation report.
4. Take a look at the iteration and the residuals of the control
points sec-tions.
Did it take fewer iterations to reach the convergence? How
many?
5. Close the Text Editor.
Task 3: Accept and Update the Triangu-lation Results
In a production environment, you could go back and forth between
removing, adjusting, or adding GCP's, and re-running the
triangulation.
For this task, we will move on to accept the triangulation.
1. Click Update and Accept, then click Close in the
Triangulation Summary.
What characteristics of the Tie points changed after
Accepting?
2. Save then Close the Point Measurement dialog.
Why have the cells under Ext. changed from red to green?
3. From the LPS dialog, select File | Save.
LPS updated the X, Y, Z, Omega, Phi, and Kappa of each exposure,
and the X, Y, and Z for the Tie Points. It also distributed the
error around the images, thereby giving us better positional
accuracy for the ortho-photo creation process.
Update to bring up-to-date the block file with the values
cal-culated during the aerial triangulation. This will update the
exterior orientation parameters (if set to Unknown or Initial), and
interior orientation parameters (if they were estimated).
Accept to confirm the triangulation results and update the X, Y
and Z tie point reference values.
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94 Introduction to LPS Section 1: Creating a Block
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ERDAS Customer Education Introduction to LPS 95
Section 2: DTM Extraction
Section Objective
This section will examine the fundamental principles and science
of extracting elevation data from stereo photographs.
Various tools and techniques will be introduced to evaluate the
accuracy of the elevation data, and verify the resulting Digital
Terrain Models (DTM).
Tools Used
DTM Extraction Tool
A component of LPS used to extract elevation mass points from a
digital block.
Contour Generation
Used to create shapefile contours of the DTM.
Change Detection Tool
Tool used for comparing images for determining differences in
pixel values.
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96 Introduction to LPS Section 2: DTM Extraction
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ERDAS Customer Education Introduction to LPS 97
Exercise 1: In Search of Z
Objective: Focus on automatic DTM extraction, which is a
capability added through LPS, and used prior to
orthorectification.
Task 1: DEM Extraction Parameters
With the triangulation results accepted and the exterior
orientation parameters updated, aerial triangulation is complete.
The next step is often ortho-generation, which requires the use of
a constant Z value, or the procurement of a DTM.
1. In the eWorkspace, click the ERDAS button and select
Prefer-ences. The Preference Editor displays.
2. Change the Category to Viewer.
3. Scroll to Background Transparent and disable this option.
This will ensure imagery displays properly in the Terrain Editor
viewers.
4. Next, change the Category to LPS.
5. Scroll to DTM Minimum Overlap Percentage.
6. Change the DTM Minimum Overlap Percentage to 30.
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98 Introduction to LPS Section 2: DTM Extraction
7. Click User Save and Close.
8. From the LPS icon panel, click the DTM Extraction icon . The
DTM Extraction dialog displays. You will be creating a DEM image
file.
9. Click the Single DTM Mosaic radio button. This creates one
output image.
10. For the Output DTM File name, type dem_20m_default.img.
11. Change the DTM Cell Size for X to a value of 20, and enable
the Make Pixels Square checkbox. The setting for Units should
remain as Meters.
12. Leave the DEM Background Value set at Default.
The cell size defaults to a value, which is approximately 10
times the spatial resolution of your image.
Generating exclusion areas in which DEM points would be
generated, a default value would be assigned as the exclusion area
elevation value.
Default Background Values will be 0 if all elevations are
positive. If there are negative elevations, a DEM Back-ground value
will be five (5) units [meters] lower than the minimum negative
value.
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ERDAS Customer Education Introduction to LPS 99
13. Click the Run button to generate your DTM.
Following are the steps involved in the generation of a DEM.
Interest Point Determination - Each image in the block is
processed to obtain a series of interest points. An interest point
is a pixel which exhibits sufficient gray level variation when
compared to a neighboring set of pixels.
After the LPS block has been triangulated, a triangle (epipo-lar
plane) can be formed between two perspective centers (X, Y, and Z),
and a ground feature. This plane is used to constrain the point
search area on the adjacent image.
An interest point located on the reference image may have more
than one possible match on the adjacent image. For each set of
possible image points identified by LPS, a corre-lation coefficient
is computed.
Epipolar Plane
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100 Introduction to LPS Section 2: DTM Extraction
Ground Point Determination - A Space Forward Intersection
technique is used to compute the 3D coordinate associated with the
mass points. This technique requires known exterior orientation
parameters.
Collinearity Equations - Used to determine initial X Y Z ground
point coordinates. The result is accurate ground coordinate X Y Z
values for all ground points.
DTM Construction - When creating an output DEM, a temporary TIN
is gener-ated, using the ground points from the above
determination. A grid (X, Y spacing) user specified, is generated
and interpolated over this temporary TIN.
A Z value (elevation value) is assigned to each grid point.
An output DEM image is generated.
Task 2: Viewing a DEM
You have created a default DEM. Later, you will compare the DEM
to one that has been generated using the Advanced Properties.
1. In a Viewer, display your DEM, and start the Inquire
Cursor.
2. Review the elevation values, then identify and make note of
any anomalous areas that may have incorrect elevation values.
3. Close the Viewer.
Task 3: Advanced Options
The use of Advanced Options will more accurately, represent the
Earth's surface when creating a DEM.
1. Repeat the steps of Task 1, but DO NOT DELETE the DEM you
just created. Instead, type dem_20m_advanced.img as the name for
the Output DTM File.
2. To open the DTM Extraction Properties dialog, click the
Advanced Properties button.
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ERDAS Customer Education Introduction to LPS 101
The Advanced Properties are divided into five categories using
the following tabs:
General
Image Pair
Area Selection
Accuracy
Seed Data
3. First, review the options in the General tab, and verify the
projection. It should be the same as the projection of your LPS
block.
4. The Horizontal Units and Vertical Units value should each be
set to Meters.
5. Enable the Create Contour Map checkbox and use a Contour
Inter-val of 5.00 (meters). The file created will be an ESRI 3D
Shapefile.
6. Enable the Remove Contours Shorter Than checkbox, and input a
value of 100. Any contour lines that are shorter than 100m will be
removed.
By default, the interval is three times that of the Output DTM
size.
By default, this is five times that of the image cell size.
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102 Introduction to LPS Section 2: DTM Extraction
7. Enable the Create DTM Point Status Output Image checkbox.
This image is a visual representation of an accuracy report, which
we will create in a later exercise. Based on correlation values
obtained dur-ing Interest Point Matching, points will be
color-coded:
Excellent = Light Green
Good = Medium Green
Fair = Yellow
Isolated = Orange
Suspicious = Red
8. Enable Reduce DTM Correlation Area by checkbox. Enter a value
of 5%. .
9. Enable Trim DTM Border by checkbox. Enter a value of 5%. The
DTM extraction area will be the full defined overlap, but will be
reduced by 2.5% on all sides.
Task 4: Choosing Image Pairs
DEMs can be generated by using all or some Stereo Pairs.
1. Select the Image Pair tab. This CellArray shows all image
pairs with an overlap of 50% or greater.
2. View your pairs by clicking the Open Viewer for Image Pair
Selec-tion icon .
3. Click the caret to view the different Stereo Pairs.
4. Select both pairs by clicking in the Row column.
5. In the Image Detail column, RMB click a cell that has 100%.
The options for this field display.
Correlation Area represents the output area of the DEM. A
reduction will reduce the DEM area from the full stereo
overlap.
Typically the outer edge of the stereo pair contains the larger
errors. By this reduction, questionable areas and fiducial areas
can be eliminated from the DEM..
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ERDAS Customer Education Introduction to LPS 103
6. For the Image Detail, select As Is to keep it at 100%. These
values indicate the last pyramid layer to be used during the DTM
mass point extraction.
On which pyramid layer does the correlation stop, if you input
the value of 25% for Image Detail?
Task 5: Area Selec-tion and Identifica-tion
1. Select the Area Selection tab.
2. The Current Pair can be changed by using the drop down menu
or the arrows. Currently the information relates to the first pair:
11_188_11_189
3. Click the Open the Viewer for Region Digitizing icon . A red
outline displays, indicating the extent of your output DEM. This
region has a Default search stragegy defined.
Since your image contains more developed urban areas, you will
add another region with a different Region Strategy. For this pair,
you will import an existing AOI.
4. Click the Load Regions from File icon , input
denver-core.aoi, then click OK.
5. In the Area Selection CellArray, click in the Row column, and
select Row 2, then RMB click on the Row number and choose Delete
Selection.
6. In the Area Selection CellArray, click in the Row column, and
select Row 2.
7. In the Region Strategy column, RMB click on the Default value
and select High Urban.
8. Click the Edit Strategies icon . Compare and make note of the
Search Size differences in both Default and High Urban.
9. Once finished examining the values, click the Cancel button
to return to the DTM Extraction Properties window.
The DTM Correlation Area may alter the AOI shape.
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104 Introduction to LPS Section 2: DTM Extraction
10. Highlight Row 1 and set the Region Strategy to Low
Urban.
The default Strategy parameters for a Low Urban can be
modified.
11. Click the Edit Strategies icon . The Set Strategy Parameters
dia-log displays.
12. Click the pull-down arrow for Strategy Name and select Low
Urban, then review the Strategy parameters.
Is the Low Urban Search Size larger or smaller than the Default
Search Size? Why?
13. Select the Low Urban strategy, and change the Search Size X
value to 19.
Changes to the Correlation size and Search size are imple-mented
by the strategy you choose.
Search Size - Window size is pixels searching along the epipolar
line.
Correlation Size - A window, which moves inside the search area
and is used to calculate a correlation coeffi-cient for interest
points.
Correlation Coefficient - A threshold under which interest
points are not used in LPS. The range is 0 to 1.
Topographic Type - Sets up internal parameters based on
topography.
Object Type - DTM extraction algorithm will function more or
less aggressively when selecting interest points. Flatter areas
requires fewer interest points than mountainous areas.
Allow Adaptive Change - LPS can make changes to the various
parameters as the DTM is computed. This may improve the results of
the strategy application. Adaptive changes take place between
iterative pyramid layer pro-cessing.
Use Image Band - Select the layer you want the correlation to
use.
DTM Filtering - High - Filters out elevation spikes and pits.
Low - Quicker, but possibly leaves more elevation spikes.
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ERDAS Customer Education Introduction to LPS 105
14. Click the pull-down arrow for DTM Filtering and select
Moderate.
15. Click OK. When prompted whether to modify Strategy
Parameters, select Yes.
16. RMB click in the Row column and choose Select None.
17. Click the Goto Next Pair arrow (down) to display the second
stereo pair. As you did previously, set the Default Region Strategy
to Low Urban.
You will now digitize the second strategy area in this pair.
18. In the Overview window, move the cursor to the bottom-right
part of your image and resize the box, if needed.
19. Click the Create Polygon Regions icon and digitize around
the downtown core area in the Viewer. The image will scroll as the
mouse is moved outside of the Viewer.
20. Double-click to close the polygon.
21. Click to select/highlight the polygon. If editing is
required, click the Reshape icon and edit as needed.
22. Change the Region Strategy of your new polygon to High
Urban.
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106 Introduction to LPS Section 2: DTM Extraction
23. Move the caret to Row 2, and then click the Edit Strategies
icon .
24. Change the Strategy Name to High Urban.
25. Change the Search Size X to 33, change the Filtering to
Moderate, and then click OK.
26. When prompted whether to modify Strategy Parameters, select
Yes.
Task 6: The Region Z
The next few steps will step through how to use the Region Z
column.
1. Digitize another polygon. It doesn't have to represent
anything, since you will soon delete it.
2. In the Exclude Area row, click on the word Undefined, then
select Custom.
For what could the Region Z Value dialog be used?
3. Click OK in the Region Z Value dialog.
4. Highlight this polygon, and then use the Cut Selected Regions
icon to delete it.
5. Click OK in the DTM Extraction Properties dialog.
By default, the Region Strategy is set to Exclude Area.
Custom is only available if the Region Strategy is set to
Exclude Area.
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ERDAS Customer Education Introduction to LPS 107
6. Click Run in the DTM Extraction dialog to create your second
DEM.
Why was the X Search Size increased in the Low Urban Strategy
parameters?
7. When the DTM Extraction is finished, go to the LPS menu and
select File | Save then select File | Close.
The Accuracy options will be examined in a subsequent
exercise.
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108 Introduction to LPS Section 2: DTM Extraction
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ERDAS Customer Education Introduction to LPS 109
Exercise 2: Visualizing Your DEM
Objective: LPS tools will be used to compare DEMs and identify
areas with questionable ele-vation values.
Task 1: Evaluate Using a Contour File
Two DTMs have been generated. The first, dem_20m_default.img,
has only default properties. The second, dem_20m_advanced.img, has
modified, advanced properties.
1. In separate Viewers, open each DTM, and list below, any
differences you see.
In your opinion, which image looks more reliable?
2. In the Viewer containing dem_20m_advanced.img, open the
shape-file, dem_20m_advanced.shp. (You will need to change the
Files of type to Shapefile.)
This is a 3D shapefile, containing X, Y, and Z values. The
contour may be difficult to see, so you will modify the colors.
3. Make sure that dem_20m_advanced.shp is the topmost layer in
the Contents pane. Then, in the Symbology group on the Drawing
tab,
select Vector Symbology , then select Automatic | Unique
Val-ues. This allows colors to be added, based on unique
attributes.
4. In the Unique Value dialog, ensure that the Unique Value is
set to Z, then click OK.
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110 Introduction to LPS Section 2: DTM Extraction
What is the range of contour values?
5. RMB click in the Row column and click Select All to select
all the rows.
6. RMB click on any of the Symbol cells, then click Other.
7. Change the Outer Color to Green and the Outer Width to 1,
click Apply, then click OK.
8. From the Symbology dialog, click Apply.
You will now change the color of individual contours.
9. Select the rows containing Z values ending in 00, 25, 50, and
75, then RMB click in the Row column and select Invert
Selection.
10. RMB click in one of the selected cells, and from the
pull-down list, change the color to Solid Red.
11. In the Symbology dialog, click Apply then Close. Select Yes
to save the changes and name the Symbology: contour.evs
How might the contours help to identify potential problem
areas?
Task 2: Evaluate Using a Relief Image
1. Open two more 2D Views. Select one Viewer, and from the Quick
Access menu, click the Open Layer icon .
2. Select dem_20m_default.img, then click the Raster Options
tab.
3. Click the pull-down arrow for Display As, select Relief, then
click OK.
4. In the other 2D View, click the Open Layer icon , select
dem_20m_advanced.img, and use the same Relief option as above, to
display the image.
In comparing the two relief images, are there differences you
had not yet noticed when viewing the DEM images earlier?
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ERDAS Customer Education Introduction to LPS 111
Task 3: Evaluate Using Change Detec-tion Tools
Until now, most of the identifiable change has been in the
downtown area, as it was more difficult to identify change in the
flatter terrain. To help better identify change, the Change
Detection tool is used.
1. From the eWorkspace, select the Raster tab, and select
Change
Detection > Zonal Change > Image Difference.
2. Input dem_20m_default.img as the Before Image, and
dem_20m_advanced.img as the After Image.
3. For the Image Difference file, type dem_diff.img, and for the
High-light Change file, type dem_high.img.
4. Change the Increase and Decrease values from the default to a
value of 1%. This will highlight within the images, any el