Surpac Dtm_surfaces Tutorial

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DTM Surfacesin Surpac Vision

January 2007

www.cadfamily.com EMail:[email protected]

The document is for study only,if tort to your rights,please inform us,we will delete
http://www.cadfamily.com/


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Copyright 2007 Surpac Minex Group Pty Ltd (A Gemcom Company). All rightsreserved.

This software and documentation is proprietary to Surpac Minex Group Pty Ltd.

Surpac Minex Group Pty Ltd publishes this documentation for the sole use of Surpac licenses.

Without written permission you may not sell, reproduce, store in a retrieval system, or transmitany part of the documentation. For such permission, or to obtain extra copies please contactyour local Surpac Minex Group Office.

Surpac Minex Group Pty LtdLevel 8 190 St Georges TerracePerth, Western Australia 6000Telephone: (08) 94201383Fax: (08) 94201350

While every precaution has been taken in the preparation of this manual, we assume noresponsibility for errors or omissions. Neither is any liability assumed for damage resultingfrom the use of the information contained herein.

All brand and product names are trademarks or registered trademarks of there respectivecompanies.

About This Manual

This manual has been designed to provide a practical guide to the many uses of the software.The applications contained within this manual are by no means exhaustive as the possibleuses of the software are only limited by the users imagination. However, it will give new usersa starting point and existing users a good overview by demonstrating how to use many of thefunctions in Surpac Vision. If you have any difficulties or questions while working through thismanual feel free to contact your local Surpac Minex Group Office.

Contributors

Rowdy BristolKiran KumarPhil Jackson

Surpac Minex GroupPerth, Western Australia

ProductSurpac Vision v5.2




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Table of Contents

Introduction ................................................................................................................................ 1Requirements ............................................................................................................................ 1Objectives .................................................................................................................................. 1

Workflow.................................................................................................................................... 1Surface Modelling Concepts...................................................................................................... 2

Creating a DTM ......................................................................................................................... 7Viewing DTMs.......................................................................................................................... 12DTM Volume Calculations ....................................................................................................... 20Applying a boundary string to trim a DTM ............................................................................... 30Sectioning a DTM.................................................................................................................... 34Draping a String Over a DTM.................................................................................................. 41Image Draping ......................................................................................................................... 43DTM / DTM Intersections......................................................................................................... 48




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Introduction

Surface Modelling allows us to use triangulation to create two-dimensional models known as

Digital Terrain Models (DTMs). This document introduces the theory behind surface modellingprocesses and provides detailed examples using the surface modelling functions in SurpacVision. By working through this manual you will gain skills in the construction, use of andmodification of DTMs.

RequirementsThis tutorial assumes that you have a basic knowledge of Surpac Vision. We recommend thatyou be at least comfortable with the procedures and concepts in the Introductory Guide toSurpac Vision training manual. If you are a new Surpac Vision user, you should go throughthe Introductory Guide to Surpac Vision training manual before going through this manual.

You will also need:

To have Surpac Vision v5.2 installed on your computer

The data set accompanying this tutorial

Basic knowledge of Surpac string files and editing tools

ObjectivesThe objective of this tutorial is to allow you to work with some Surface Modelling tools. It is notintended to be exhaustive in scope, but will show the work flow needed to achieve results.You can then refine and add to this workflow to meet your specific requirements.

Workflow

1www.cadfamily.com EMail:[email protected]



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Surface Modelling Concepts

A digital terrain model (DTM) is made up of a surface joining adjacent strings. It is formed as

a combination of those string lines, and of lines joining points on strings.

The joining process continues until the surface consists only of non-overlapping triangles. Thesoftware chooses the joins to produce the best-conditioned triangles - ie. those closest toequilateral triangles.

The resulting DTM can be thought of as an undulating patchwork quilt made up of triangularpatches.

A Digital Terrain Model (DTM) is how Surpac models surfaces. Surfaces are used in Surpacfor such things as 3D visualization and for calculating volumes. Almost any superficial featurecan be modelled as a DTM, including natural topography, lithological contacts,

bedrock/overburden contact, or water tables.




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DTMs must come from String data. String files contain the raw data, whereas DTM filescontain a mapping of trios of points in the String file that constitute a triangle.

DTMs are made of triangles, with each point of each triangle matched to a point in the originalString file. Consequently DTM files are not valid without the original String files. That is, aDTM file cannot be opened if the original String file of the same name is not accessible.

Another rule for the construction of DTMs is that DTMs cannot fold back on themselves. Thatis, a DTM cannot have multiple Z values for a given X, Y coordinate. Therefore you cannotmodel overhanging or vertical surfaces.

If the surfaces are to be used for further processing, such as for calculating volumes or higherend functionality within the surface menu, then the object must be named object 1 trisolation 1.It is important to consider this when creating the surface, as each surface must then beplaced in a separate file.

1. Nomenclature

The objects you create in Surpac Vision are numbered by a system analogous to that of stringand string segment numbers.

String object

Segment trisolationPoint triangle

When you define an object you explicitly assign it both an object number and a trisolationnumber. The object is then always referred to by the object and trisolation number originallyassigned.

The object number may be any in the range of 1 to 32000.

The trisolation number may be any positive integer.




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DTM Conventions:

DTMs cannot model overhangs or vertical surfaces

DTMs must have one surface to a layer

You must differentiate between spot heights and breaklines

Firstly we will look at the use of strings to act as break lines. Breakline strings are those whichrepresent physical features that you can see in the real world e.g. crest of a pit, a fault in ageological model, a contour in a pit.

If a string file has been formed correctly, then no breakline strings will cross over otherbreakline strings, unless the two strings cross at a common point as shown below.

Spot height strings contain random points which, when connected by a string line, do notrepresent any physical feature eg. randomly surveyed points, borehole collars.




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When modelling surfaces with DTMs, it is important that no triangles are formed across anybreakline strings. If however, the string data consists of spot heights only, then the triangleswill be formed in the most robust manner without taking into account any strings between thepoints.

2. Graphical vs File-based options

A digital terrain model can be created in two ways to best suit the data you wish to model.

Graphical creation of a DTM allows you to view your results immediately, however, for largedata files the processing time may be prohibitive. The file-based tools allow you to performthe creation directly on the file data, saving both memory usage and creation time.

The diagrams below show how to choose the functions used to create DTMs, firstly from agraphics based function, then for a file-based function




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Creating a DTM

Overview

It is important to understand how a string file relates to a dtm. Once a dtm has been created,any modifications to the string file will make the DTM invalid. Hence, if modifications aremade to string data, you will need to recreate the DTM.

1. Graphical Creation

Open the file topo1.strin Graphics

From the Surfacesmenu, select Create DTM from layer.

ClickApplyon the form to create a DTM surface.

Since the data you are working on is a copy of the original data, the file must always be savedafter the DTM creation.

From theFilemenu, select Save, then String/DTM, to save the DTM file

Enter the data as shown below, then clickApply.




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Because the string file and dtm already exist, you will be asked if you wish to replace them.Click Yes.

Your results should like the diagram below:

If you want to see all of the steps performed in this chapter, either run or edit:

_01a_create_DTM_from_layer.tcl

Note: You will need toApplythe forms presented.




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2. File based DTM creation

We will now create a DTM from the string file pit1.strusing the file based DTM creationoption. We will use this function to demonstrate the impact of using strings as breaklines.

From the Surfacesmenu, select DTM File functions, then Create DTM from string file.

Fill in the form as shown below, then clickApply.

Note: The Strings to act as break lines checkbox is NOT ticked

Note: The ability to clip to a boundary string at the same time as creating the DTM is new

functionality introduced in Surpac Vision V5.2D. In earlier versions, or if you wish to clip aDTM from a string file after the DTM has been created, use the function Clip DTM fromboundary string under the DTM file funct ions menu.




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Open the file pit1.dtmin Graphics. You should see something similar to that shown below:

Note that there are several triangles in the dtm that do not reflect the results we desire.We will now repeat the procedure, but using strings to act as breaklines.

From the Surfacesmenu, select DTM File functions, then Create DTM from string file.This time ensure that the checkbox for Strings to act as break lines is ticked.

Fill in the form as shown below and clickApply.

The message window informs you of the processing as the DTM is created. When

processing is finished, you will see a log file, which is a small report containinginformation about your DTM. Close the file to continue.




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Viewing DTMs

1. Colour a DTM by Elevation

Open the file pit1.dtmby dragging it into Graphics.

From the Displaymenu, select DTM with colour bandingto display colour contours.

Viewing the DTM by drawing shells is another method of displaying DTMs. Drawing shellsand using false colouring of triangles is very similar to contouring your data. You cannominate to draw shells by:

specifying the number of bands

setting the band width

Enter the parameters on the form as shown below and clickApply.

As you have nominated to display bands every 20 metres, the image on screen representsthe following:

blue 0 to 20 metres

green 20 to 40 metres

yellow 40 to 60 metres

red 60 to 80 metres and then the colours repeat and so we have

blue 80 to 100 metres and so on




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Your result should look something like the image below:


_02_colour_DTM_by_elevat ion.tcl

Note:You will need toApplythe forms presented.




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2. Creating a Fly-through Movie

We will now digitise a string to follow and use the View along st ringfunction which allows usto effectively fly in the direction of the string. This is an excellent method for viewing terrain

models.

Reset graphicsby clicking on the icon.

Drag and drop the file eom_pit.dtminto Graphics.

First, we will apply colour banding to produce a realistic effect for our DTM display. Fill outthe form as shown below, then clickApply.




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Now we will exaggerate the relief to make the flythrough more realistic. From the View menu,select Data view options, then View scale factors.

Fill in the form as shown below, then clickApply.

You will now digitise the line that you wish to fly along. The first step is to set the stringnumber for any digitising that will be done. On the status bar at the bottom of the screen,

click on the design string icon .

Set the string number to 500, then clickApply.

Next you will create a new layer for the new digitised string.

On the toolbar, select the layer selection box, and click on the option.




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Enter the name of the new layer as shown below, then clickApply.

The digitised string will be placed into this layer.

The final step before you start creating your line is to tell Surpac that when you digitise a pointit should snap onto the DTM surface. From the toolbar, select the snapping list options andclick on the Triangleoption.

Now you are ready to digitise your line. On the toolbar, select the icon. Now you candigitise your line. If you wish to window in you can do so at any time, and then start thedigitising again by clicking on the icon again.

Once you have digitised your line, you should save the string file. Save the file as fly1.str. It isalso useful to smooth the string out. This will remove any sharp turns in the line.

From the Editmenu, select String, then Smooth. Fill in the form as shown below, then clickApply.

Save the file again. Now you can run the View along stringfunction. From the Viewmenu,select Data view options, then View along a str ing.




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This will display a form with the viewing options.

Select the along string optionon the left. In the middle of the form, enter a camera fieldwidth of 100, a Camera Z offset value of 20 to lift the camera 20m above the ground and aMax frame distance as 5. The bigger this distance, the faster the camera will move along thestring.

Click on theApplybutton and then click on the first point of the fly string.

Any time you wish to run the animation again, click on Zoom All, and then go to the Viewalong stringfunction as shown earlier.


_03a_fly_through.tcl


Saving the images to make a movie.




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Run the View along st ringfunction again, but this time on the right of the form, enter a nameto be given to the images that will be saved at set points

Note: This process will produce many output files so we have changed the Max. framedistance to capture an image every 20 metres.




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You can set the number of pixels to higher resolutions than the default if required. This willcreate better images, but will also create bigger files for each image. This option creates avery large number of files, so be careful about how much memory you have free on youcomputer.


_03b_fly_through_save_images.tcl





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DTM Volume Calculations

1. Create a boundary str ing

We will now look at creating a boundary string of the pit to be used in volume calculations.

A boundary string file can be used for:

delineating cut and fill material for calculating volumes

finding the intersection of a fault plane with a surface

finding where a pit design breaks the natural surface.

There are two ways to create the boundary string in Surpac Vision, either file-based orgraphics based. In the file-based method, there is no need to display the DTMs and theboundary string is automatically saved to the nominated file. In the graphics-based method,the DTMs must be displayed in graphics and the boundary string is not automatically saved

but is simply displayed in its own graphics layer. You must save your boundary string to a fileafter it is generated.

File-based method

Firstly, we will look at the file-based method. In this case, we will display the DTMs only forclarity.

Open the files pit1.dtmand topo1.dtmin graphics.

Note that the pit extends past the natural topography. To determine the volume of the pit, weneed to define the boundary where the topography cuts the pit design, otherwise our volume

estimates will be incorrect. We do this by creating a boundary string of the intersectionbetween both DTMs.

From the Surfacesmenu, select DTM File functions, then Line of intersection betweentwo DTMs.




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Once we have the boundary string we can use it to constrain our volumes calculation.

On the form below, fill in the names of the DTM files you wish to find the intersection of, thendefine the output string file you wish to create. Complete the form as shown below, then clickApply.

Once this for has been processed, a message will appear in the message window and thestring will be displayed in graphics


_04a_create_boundary_string_fi le_based.tcl

Note: You will need toApplythe forms which are presented.




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Graphics-based method

This process can also be completed graphically. In this case we MUSThave the DTMsdisplayed in graphics as the function uses graphics layers to determine its input and output

Open topo1.dtm and pit1.dtm in graphics

From the Surfacesmenu, select Clip or intersect DTMs, then Line of intersectionbetween two DTMs. Complete the form as shown below, then clickApply.

This outputs the same result as the file based functions, but the fields can be selectedgraphically. In the graphics-based method, you need to save the string in the intersectionlayer to a string file if you wish to use it for further processing.

After applying this form the result is displayed in the graphics and should look something likethe diagram below:


_04b_create_boundary_str ing_graphics_based.tcl





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2. Cut and Fill Between DTMs

We will now use the function Cut and fil l between DTMsfunction from the Volumesmenu tocalculate the surface-to-surface volume between pit1.dtmand topo1.DTMand create a

resulting volume report.

One of the most common uses of DTMs is to calculate volumes. The DTM Volumes functionallows you to compute the volume between two DTM surfaces, contained within a boundarystring.

From the Volumesmenu, select Cut and fil l between DTMs. Fill in the form as shownbelow then clickApply.

You should see something like the following:




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Create a DTM of the file dhc2.strwhich is a survey of drill hole collars prior to mining and will

be used to model the natural surface.

From the Filemenu, select Reset graphicsor click on the icon.

Open the string file dhc2.strby dragging it into Graphics.

This file is a survey of drill hole collars prior to mining and may be used to model the naturalsurface. Notice that the file consists of one spot height string.





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Complete the following form:

Note that when creating a DTM by the file based method, we can turn off the option 'Strings toact as break lines. The result is saved as dhc2.dtm.

We will now create a DTM of the file pit2.strusing spot heights and using the breaklinetest

Load the file pit2.strin graphics and display the string numbers to determine if there are anyspot height strings. String 9999 consists of spot heights and can be used during the creationof the DTM.





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Complete the following form:

The result is saved as pit2.dtm.

Using these two files, we will calculate the volume between the two surfaces.

From theVolumesmenu, select Net volume between DTMs. Enter the parameters asshown below, then clickApply.

Note: String #2 of pit2.str can be used as a boundary string for the volume calculation.




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Complete the form shown below, then clickApply.This defines the output file name andformat for the report.

Applythe blank form as shown below:

The results from the DTM volume calculations can be saved to a .csv file and optionally to aboundary string file.

This string file contains details of the calculations in the Description Fields. The results thatare saved to the D fields and the order in which they are saved are described below. Thesevalues can be found starting with the D1 field.

slope area of first DTM

slope area of second DTM (only if 2 DTMs are used)

area of boundary segment

volume between 2 DTMs (or between the first DTM and datum plane z=0)

average thickness (volume/area of boundary segment)

total of first quality parameter (if it is used)

average value of the first quality parameter (only if it used)

total of the second quality parameter (only if it is used)

average value of the second quality parameter (only if it is used).

Next you will be prompted to save the modified files.

Save the modified DTM.




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Because you use a boundary string to calculate DTM volumes, triangles which lie outside theboundary string are deleted. Hence the prompt to save the modified DTM. The first DTM isdhc2and there is no point in saving this file, so simply Applythe blank form.

Once again a prompt to save the modified DTM is presented, this is for the second DTM pit2.

Applythe blank form as we do not need to save this file.


_05_cut_and_f il l_volumes.tcl





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The volume report results shown below are in the file pit2.csv, which will be displayed on thescreen.




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Applying a boundary string to trim a DTM

This function uses a boundary string to trim a DTM. The boundary string may consist of any

number of closed segments and may contain clockwise and internal anticlockwise segments,(i.e. representing pillars or waste volumes). This function is used to prepare a file for viewingin solids modelling or contouring within a restricted area.

1. File Based Method

Firstly we will look at applying a boundary string to trim a DTM using file based data.

From the Surfaces menu, select DTM File functions, then Create DTM from string file. Fillin the form as shown below, then clickApply.

In this case, we are using the same string to clip the dtm as was used to define the boundaryof the dtm. Since the operation was performed directly on the input files, there is no need tosave the DTM file.

Open the file back1665.dtm by dragging it into Graphics. You will see that the DTM hasbeen clipped to the borders defined by theback1665.strstring file.

The ability to clip to a boundary string at the same time as creating the DTM is newfunctionality introduced in Surpac Vision V5.2D. In earlier versions, or if you wish to clip aDTM from a string file after the DTM has been created, use the function Clip DTM from

boundary string under the DTM file funct ions menu.





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_06a_clip_dtm_fi le_based.t cl

Note: You will need toApplythe form which is presented.

2. Graphics based method

Now we will look at a method that uses the data displayed in graphics to clip the DTM.

Note that the file lev1665.str represents the same data as in back1665, but dropped 6 metresin the z direction using string maths.

Open the string file lev1665.strby dragging it into Graphics

Rotate the image within graphics to view the file. It should look like the image below:

This represents the pickup of some underground workings.

From the Inquire menu, select Segment properties, and select a number of points on thestring, note that the pillars are all anti-clockwise and the drives are all clockwise.

From the Surfacesmenu, select Create DTM from layer andApplythe confirmation form.




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Save the resultant DTM to a file lev1665.dtm.

Note that when the DTM was created, no distinction was made between clockwise or anti-clockwise strings. The result is a rather untidy DTM which does not properly model theoriginal survey data. By using the floor string as a boundary string, the anti-clockwise

segments will act as areas of exclusion The DTM Clip function does exactly this.

From the Surfacesmenu, select Clip or intersect DTMs, then Clip DTM with st ring.

Select a point on the string to perform the clipping operation. Save the resultant data to DTMfile lev1665.dtm.




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Note how the triangles outside the boundary strings have been clipped. This is one way ofbeginning to create a 3D model of these underground workings.


_06b_cl ip_dtm_graphics_based.tcl





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Sectioning a DTM

This function allows you to create horizontal, vertical or inclined sections through a surface

The plane of intersection of the sections is defined by entering the Y, X, Z coordinates at eachend of a three dimensional axis line and by specifying the interval along that axis at whichsections are to be taken. The first section is taken at the start of the axis and then sectionsare taken at the specified intervals along the axis until the length of the axis is reached.

1. Create DTM sections

Open the file pit1.dtmby dragging it into Graphics. From the Createmenu, select Sectionaxis by coordinates. Fill in the form as shown below to create a section axis line.

From the Surfacesmenu, select Create sections from DTM. Fill in the form as shown below

and clickApply.




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Then fill in the next form ( or accept values from previously defined section axis line) to definethe axis line and clickApply.

Note: The axis start is the co-ordinates for the starting point of the axis line. The first sectionis extracted at this starting point.

The axis end is the end point of the axis line. Sections may be extracted either perpendicularto the line defined by the start and end points or parallel. Sections will not be extracted past

the axis end point.

The result produced by this function is a range of string files, named dtm_section7000 todtm_section7600 in steps of 100, which contain the extracted sections in section coordinates.These files are automatically saved to disk.

You should see something like the diagram below. Note that the axis line is displayed in theleft pane. In the right pane are the resulting sections, displayed in section coordinates.

The segments produced from the Create sections from DTMfunction will have the samestring number as the object number from which they were extracted. The segments producedmay be either open or closed segments. Closed objects will always produce closed segmentswhen they are sectioned, whereas open objects may produce either open or closed segments.Closed objects are significant, because the sections generated from sectioning a closed

object can automatically be used for further processing where closed segments are required.




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There is also a file-based sectioning function. It may be accessed through the Surfacesmenu,by selecting DTM File functions, then Create sections from DTM. This function removesthe need to load DTM files (which can be very large) into Graphics

The diagram below shows how to invoke the file based version.


_07a_create_sect ion_axis_line.tcl_07b_sectioning_pit .tc l


2. Create DTM contours

We will now look at how to section the pit by elevation, creating contours every 10 metes on

the file pit1.dtm.

Open the file pit1.dtmby dragging it into Graphics. We now wish to extract or create contoursby elevation for every 10 metres within the pit.

Optionally, you can click on the icon to plot a 2D grid over the area if you want todetermine the minimum and maximum extents of the pit. Note that the form automaticallyshows that the elevation of this DTM goes from 45 to 245 metres.

From the Contouringmenu, select Contour DTM in layer. Fill in the form as shown belowand clickApply.




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If you wish to save the sectioned string file, change your active layer to sectionand thensave the file.




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_07b_section_pit_by_elevation.tc l


3. Contour Extract

This function extracts contours from a DTM and then stores them in a string file for viewing orplotting. The contours are created by interpolating line segments across all of the trianglesand then joining them into continuous strings. The contours will exactly correspond to theoriginal data from which the DTM was created.

These contours can then be used for plotting or for volume calculations or polygonintersections with other string files.

If contours are required for volume calculation or polygon intersection they mustbe closedstrings. You must ensure that the original DTM is constructed so as to guarantee this will

happen.

Usually this will involve adding an extra boundary string enclosing the string data within theDTM but with a Z value just greater than the maximum Z value in the data (in the case of apit,) or just less than the minimum Z value in the data (in the case of a stockpile).

We will now look at an example. From the Contouringmenu, select Contour DTM file. Fill inthe form as shown below , then clickApply.




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Fill in the form as shown below and clickApply.

Define the method that you wish to create the contours.

Interval:The contours to be extracted will be defined by entering an interval with a minimumand maximum contour value.

Range: The contours to be extracted will be defined by entering a range. Unlike the Intervalmethod which guarantees that contours will be at integral multiples of the contour interval, thismethod permits you to define the contour levels of interest precisely. It is therefore possible tocreate contours at intervals of 2 but starting from a non-integral multiple of 2. e.g. 147.5,149.5 etc.

This method also permits you to extract contours at irregular intervals thus making it possibleto extract contours at values of particular interest.




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Define the plot enhancement requirements

Create index contour file

If you intend to use the contours for plotting, you may wish to plot the index contours (orcontours at some specific interval) in a different colour to other contours. For example, if

contours were extracted at intervals of 2, then index contours would probably be at intervalsof 10, that is 10, 20, 30, etc.

These index contours may be saved to an Index contour string file thus making it easy to plotthe index contours using a different colour on a hardcopy map.

If you choose to create an index contour file, then the index contours will not be in the contourstring file at all, they will only appear in the index contour file.

Produce contour annotations

If you choose to create contour annotations then a string file will be created which contains

data suitable for use by the Plotting module for labelling the contour strings, at the mid pointof the each contour, with the contour values.

This string file will consist of pairs of points. Each pair of points will be aligned with a smallportion of the contour string, in the middle of the string, with the contour value in the D1 fieldof the second point in each pair of points.

String 1 in the annotation string file will contain all the annotation data for the Normal contourswhile string 2 will contain the annotation data for the index contours.


_08_extract_contours.tc l





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Draping a String Over a DTM

Open the file topo1.dtmby dragging it into Graphics. Also open the file dhcollar1.str in

graphics. From the Customisemenu, select Display properties, then Strings and points.

Change the drawing method to marker as shown in the form below to display the string asspot heights.

Note that the drillhole collars are currently at an elevation of 300m.

To determine the correct elevation of the drill hole, we will drapethe drill hole collars onto thetopography to determine the point of intersection.

From the Surfacesmenu, select Drape str ing over DTM.




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Click on one of the markers to select the string to drape over the DTM. Ensure that youuncheck the Interpolate New Pointscheckbox in the form presented.

Your results should look something like the image below. Note how the drill holes have nowbeen draped over the topography.


_09_drape_string_over_dtm.tcl





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Image DrapingThis function permits you to apply advanced rendering techniques to DTMs by draping animage file over the model. Surpac allows you to use GIF, jpeg, tif, png or bmp files as images

to drape over your DTM.

This technique is very useful:

When an aerial photograph has been scanned and saved in a image file and you

wish to drape it over a DTM of the surface to give a photo-realistic representation of

the land surface. This technique requires you to digitise a number of control points,

known as registration points in the image and in the DTM.

When you want to display solid models of ore bodies with a texture appropriate for

rock type which it represents. In this case, you require a image file of a suitable

texture which is then 'tiled' over the model.Note: This technique requires some effort to produce good results. Matching points in theimage and the DTM must be selected with care, otherwise the image will not match the DTM.The co-ordinates of the control points may be saved to a registration file (.rgf) to simplifyfuture image rendering.

Open the file eom_pit.dtmby dragging it to graphics.

From the Filemenu, select Images, then Drape an Image file over a DTM.

The prompt at the bottom of the screen will say ask you to Select the triangle of interest .

Select a triangle on the trisolation to which the image file is to be applied to display the DrapeImage over a DTM or Triso lation form as shown below:

The registration file stores the parameters used for registering a image file over a DTM so thatthe image can be made to match the DTM precisely. In addition to the name of the image file




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and the filter colour, the registration file records the image coordinates (X and Y pixel values)and the corresponding real world coordinates for each of the registration points.

If you are using either of the tiling options then any file name which you might enter into thisfield has no effect on the result.

A minimum of 3 registration points are required and a maximum of 100 can be used. As moreregistration points are used, the image will develop a progressively better match with the DTM.

Enter a name to create a new registration file.

If the registration file named does not exist then it will be created and all the details are savedto it after the registration points have been defined.

If the registration file already exists, the parameters are displayed on the form to permit you toalter them to suit your requirements.

Registration files are commonly used to simplify the task of draping an image over a DTM asdefining registration points repeatedly for the same image/DTM can be quite time consuming.

Image file

This is the image file which contains the image to be draped over the DTM.Image draping method

The image can be draped over the trisolation using one of two different methods, with eachmethod having two variations. These methods are:

1. Registering the image.

This is where the image and the DTM over which it is to be draped are displayed side by side,in different viewports. Matching pairs of points are selected, using the mouse, to control the

process of draping the image over the DTM.

This method is most suitable when the image is of an aerial photograph and the DTM is theland topography at the time the photograph was taken.

The two variations for this method are:

register with new pointsThis method will use whatever registration points are displayed in the registration pointsscrolling region and will require more registration points to be defined. You may find that thismethod will be used a number of times with an image and DTM to progressively improve thematch between the image and the DTM.

register with existing pointsThis method will only use the registration points displayed in the registration points scrollingregion. If fewer than 3 registration points are present in the scrolling region when you clickApply, you will be required to define some more registration points.

2. Tiling the image

This is where the image is given dimensions, in the real world X and Y directions, and theimage is tiled over the selected trisolation in tiles of these dimensions.

This method is useful for applying images of different material textures to make solid modelsof ore bodies, for example, appear more realistic. The best results will be achieved with

images which have no obvious pattern especially when tiling over solid models as the imagemay be distorted considerably when folding underneath the solid model.




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The two variations for this method are:

tilingThis tiling method simply places the image in tiles of the specified size over the trisolation.

mirror tiling

This tiling method creates a mirror image of every second tile, in both the X and Y directions.

Define registration points by

When using registration points, you always use the mouse to select the registration pointlocations in the image. To define the registration point coordinates in the DTM however youmay choose from:

Graphics

The mouse is used to select the location of the registration point on the DTM. Use thismethod when only approximate locations for the registration points are known or whensurface features, roadway intersections for example, are being used.

Keyboard

The coordinates of the registration points are entered into a form. This method is appropriatewhen the registration points are surveyed targets which are clearly identifiable.

Transmission colour

The textured image may be made transparent by specifying a transmission colour. This colouris allowed to shine through the textured object when another object falls behind it. Best resultscan be obtained by using grey.

Ambient colour

Some graphics cards adaptors may cause a dimming of the textured image. This can becountered by specifying an ambient colour that is reasonably light in colour.

To cancel the effect of the transmission colour and ambient colour as applied by the ImageDrape function, you can use either the Clear Screen or Erase Objects functions.




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Image colour filter

The image colour filter works in a manner similar to colour filters in photography. By leavingthe colour filter blank, the image is presented in the colours as defined in the image file.

Image and Real World coordinates fo r registration points

If an existing registration file is being used, all the saved parameters, including previouslydefined registration points are displayed here. There must be a minimum of 3 registrationpoints to register the image to the DTM with the maximum number of registration points being100.

Complete the Drape Image over a DTMor Trisolationform and clickApplyto either drapethe gif image over the selected trisolation or to define registration points for controlling theimage registration process.

The registration points must now be defined by selecting a location in the image.

Digitise the registration point # in viewport 2

Locate the mouse over the required point in the image and press the mouse button to definethe image coordinates for a new registration point. The following prompt will be displayed:

Digitise registration point # on the DTM in viewport 1

Locate the same point in viewport one and press the mouse.

After digitising the location of the registration point in the DTM or entering the coordinates ofthe registration in the Define coordinates for image registration point form, you will beprompted to digitise another registration point. When sufficient registration points have beendefined, press Escapeto display the Review registration point coordinatesform.

These are the real world coordinates of the corresponding locations for registration points inthe DTM.

Complete the Review registration point coordinates form and chooseApplyto drape theimage over the selected trisolation.


_10_image_draping.tcl





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Helpful Hints

Adjust ing the view

When defining the registration points either in the image or in the DTM, it is generallynecessary to adjust the view by either windowing in or out to find the best location for the

registration point. By pressing theAssist key, generally F11you can invoke the Viewertoadjust the view. On exiting from the Viewer, you will be prompted to select the point of interest.

Resizing the viewports

The original viewport containing the selected trisolation is split vertically so the image andtrisolation can be displayed side by side. You may find that the viewports are too small. It ispossible to resize and move the active viewport while in the midst of a point digitise action ifyou find it necessary to alter the viewport size and/or location. If the two viewports overlapthen the viewport in which the point must be digitised is brought to the front when necessary.

Finding the registration points

It is generally easier to locate the position of registration points in the DTM if the image hasbeen rendered with a Light Sourcebefore starting the process of defining the registrationpoints. This is because surface features are much more obvious when rendered with a lightsource and easier to relate to the image.

Memory usage

Image files, especially if they are large, can consume a considerable amount of memory. Toestimate the memory requirements for displaying an image, use the following formula:image memory usage = X pixels * Y Pixels * 3 bytes

Therefore, an image which is 1000 pixels square will require of the order of 2.5 Mb of memory.


_10_image_draping.tcl



http://../Documents%20and%20Settings/pjackson/ssi_V5.0-K/share/refman/default/graphics/viewer.htmhttp://../Documents%20and%20Settings/pjackson/ssi_V5.0-K/share/refman/default/graphics/lighton.htmhttp://www.cadfamily.com/http://../Documents%20and%20Settings/pjackson/ssi_V5.0-K/share/refman/default/graphics/lighton.htmhttp://../Documents%20and%20Settings/pjackson/ssi_V5.0-K/share/refman/default/graphics/viewer.htm


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DTM / DTM Intersections

1. Upper triangles of 2 DTMs

This function takes two DTMs as input and creates a new DTM, which is an upper surfacecombination of the two input files.

We will now look at combining a DTM representing a proposed waste stockpile and a DTMrepresenting the topographical ground profile to produce a new DTM of the ground profilecontaining the waste stockpile.

Open the two DTMs called topo_dump1.dtmand dump1.dtm, appending them both into thesame layer. These represent a topographic surface and a dump surface model.

From the Surfacesmenu, select Clip or intersect DTMs, then Upper triangles of 2 DTMs.The DTM/dtm Upper Results Storageform is displayed. You are prompted for a layer name

in which to display the resultant DTM and the object number to assign to this DTM.

Enter values of your choice, e.g. combined_surface, object number 1. The layer name cannotbe the same as any of the current layers.

Now follow the prompt by picking each of the DTMs. The order of selection is not important.The program will go through the process of joining the two DTMs, finishing with the statementCalculations are completed. You will now be in the layer you specified with the resultantDTM displayed. The result is a DTM of the waste stockpile surface incorporated into thetopographic surface.


_11a_upper_triangles_of_2DTMs.tc l





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2. Lower triangles of 2 DTMs

This function takes two DTMs as inputs and creates a new DTM, which is a lower surfacecombination of the two inputs.

We will now look at combining a DTM representing a proposed pit design and a DTMrepresenting a topographical ground profile to produce a new DTM of the ground profilecontaining the pit design.

Open the two DTMs called topo1.dtmand pit1.dtm, appending them both into the samelayer.

These represent a topographic surface and a pit design surface model.

Go through exactly the same process as described in the previous exercise except chooseLower triangles of 2 DTMs. The result is a surface representing the pit incorporated into thetopography.


_11b_lower_triangles_of_2DTMs.tc l

Note: You will need toApplythe forms presented.




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3. Create sol id by intersecting 2 DTMs

This function takes two DTMs as inputs and creates a 3DM, which is the volume enclosedbetween the intersection of the two DTMs.

We will now look at combining a ground terrain profile with a proposed pit profile to find thevolume of material which must be extracted to create the pit.

Open the two DTMs calledtopo1.dtmand pit1.dtm, appending them both into the samelayer. These represent a topographic surface and a pit design surface model.

From the Surfacesmenu, select Clip or intersect DTMs,then Create solid by intersecting2 DTMs

The DTM/dtm Intersect Results Storageform is displayed. You are prompted for a layername in which to display the resultant DTM and the object number to assign to this DTM.

Enter values of your choice, e.g. layer_intersect, object number 1. The layer name cannot bethe same as any of the current layers.

Now follow the prompt by picking each of the DTMs. The upper DTM (topography) must be

selected first, followed by the lower DTM (pit). The program will go through the process ofjoining the two DTMs, finishing with the statement Calculations are completed.

You will now be in the layer you specified with the resultant 3DM displayed. The result is asolid 3DM representing the material that will have to be removed from the designed pit. Theimage below shows before and after the DTM/DTM Intersection.

From the Solidsmenu, select Solids toolsmenu, then Report volume of solidsto create a

note file with the volume of the Pit below the topography.




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_11c_create_solid_intersecting_2DTMs.tcl


Summary

String file (*.str) contains spatial data

A DTM is a digital terrain model which is an indexed list of triangles which contain nospatial data

A DTM file is invalid without its associated string file

Triangles are referenced in 3-D space by points in strings and the triangles areformed by connecting groups of three data points together by taking their spatiallocation in the X - Y plane into account.

Vertices of triangle coincident with a string point.

Uses:

Surface to surface volumes

Model weathering surfaces, topography

Visualisation

Extract sections and plans

Conventions

One DTM surface per file

Breakline v SpotHeight

No vertical or overhanging surfaces

String file hierarchy DTM file hierarchy

String ObjectSegment TrisolationPoint Triangle

Breakline strings are those strings which represent physical features that you can seein the real world e.g. crest of a pit, a fault in a geological model, a contour. Nobreakline strings should cross over other breakline strings, unless the two stringscross at a common point.

The breakline test is an important concept to understand if DTM is to accuratelymodel terrain

Spot heights are random points so will triangulate nearest neighbour