1107 NW Oak Av Corvallis OR 97330 Ph: 541-754-3488 Fax: 541-738-2934 Global Mapping Technology Products and Training for GPS/GIS/SURVEY GMTGPS .

1107 NW Oak Av Corvallis OR 97330Ph: 541-754-3488 Fax: 541-738-2934

Global Mapping Technology

Products and Training for GPS/GIS/SURVEY

GMTGPS www.gmtgps.comemail: gmtgps@peak.org

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Global Mapping TechnologyProducts and Services

GPS/GIS and GPS SURVEY PRODUCTS GPS MAPPING SERVICES

LASER RANGE FINDER MAPPINGGPS/GIS TRAINING

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The Global Positioning SystemA Constellation of Navigation

Satellites Orbiting the Earth

The Global Positioning SystemA Constellation of Navigation

Satellites Orbiting the Earth

GPS is operated and maintained by theUnited States Department of Defense

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How is GPS technology used?

• GPS is used to determine position

• Latitude, Longitude, Altitude

of an object• Applications range from navigation

to data collection for GIS/Mapping

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What is GIS?

• Geographic Information Systems

• GIS allows us to create maps

• GIS provides tools for analyzing geographic information

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How do GPS & GIS work together?

• GPS technology is used to determine the position of an object

• GIS can be used to describe & map geographic objects

• GPS for GIS means that GPS technology is used to collect GIS information - descriptive information about objects in specific locations

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GPS/GIS ApplicationsForestry/Agriculture/Natural Resources

• Timber Cruising

• Acreage Determination/Precision Farming

• Habitat Evaluation

Utility/Municipal

• Utility asset mapping

• Roads, Property Lots, etc...

Surveying/High Precision GPS

• Construction Stake Out

• Road Design

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Example of GPS/GIS collection(Step 1 and Step 2)

1. GPS/GIS unit used to collect Feature records:

- Location of objects (GPS)

- Description of the object (GIS)

LAT: 44 32 45.5611N LON: 123 14 22.1661W HAE: 63.5 Meters

Tree, Species: Fir, Stand No: 1,

2. Information from GPS/GIS unit is downloaded to a GPS/GIS program.

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3. In the GPS/GIS program, differential correction may be performed to improve accuracy of GPS coordinates.

Example of GPS/GIS collection(Step 3 and Step 4)

4. A finished map, complete with symbols and labels, is created.

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Specifics on GPS Technology

- GPS System Overview

- How GPS receiver calculates position

- How accurate is GPS

- What affects GPS accuracy

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GPS system was developed by the US Dept of Defense for military positioning applications. GPS is now widely used for civilian applications.

GPS System OverviewThe GPS system is comprised of three “segments”

Space Segment:

Control Segment:

User Segment:

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Space & Control Segment

Space Segment

• 24 active satellites, 3 spare satellites

• Orbit at ~ 20,000 km; 1 revolution per 12 hours

• Broadcast radio signals - signal travels at the speed of light

Control Segment

• 5 Monitoring & Upload stations

• Receive and Transmit information to SV

• Ensure accuracy of SV position & clocksCopyright CMT, Inc.

Satellites also called “SVs” or Space Vehicles

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User Segment

•GPS receivers track satellites and use SV signal information to calculate:

- position, velocity, time

“GPS receivers” are used in a variety of military and civilian applications.

The term “tracking satellites” means that the GPS unit is receiving radio signals being broadcast by satellites.

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1) Receiver tracks a number of Satellites (SV).

2) Receiver knows each SV position based on ephemeris in the SV signal.

3) Receiver determines distance or “range” between the SVs & itself. (Signal “travel time” x Speed)

4) Receiver uses trilateration to calculate its position.

How GPS Receiver calculates position

The more accurately a GPS receiver measures the ranges, the potentially more accurate the calculated positions. Different types of GPS receivers use different measurement or “positioning” methods to determine ranges.

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Trilateration: Receiver must track at least Four Satellites to calculate 3-D position

• 3-D position is: Latitude, Longitude, Altitude

• GPS receiver must “solve” for X, Y, Z and time.

• If GPS unit is only tracking 3 SV, 2-D position will be computed. (XY)

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How Accurate is GPS?

• GPS provides 50 - 100 meter accuracy.

• Accuracy can be improved by Differential Correction.

• Corrected Accuracy depends upon the type of GPS positioning method.

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GPS Error BudgetAn uncorrected GPS position usually is accurate to 100meters (2 RMS). This error comes from many sources,several of which are listed below. Some of the error canbe removed by Differential Correction.

Source Removed by Differential Correction

Ionosphere PARTIALLY REMOVED

Troposphere YES

Measurement Noise YES

Ephemeris Data YES

Satellite Clock Drift YES

Multipath NOT REMOVED

Selective Availability (SA ON) YES

Uncorrected error with SA ON: 100 meters (2 RMS)

Uncorrected error with SA OFF: 38 meters (2 RMS)

Error after Differential Correction: 5 meters (2 RMS)

Range of Error Occurring 95% of the time

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Differential Correction Removing GPS Error

• Post-processing Differential Correction In many GPS mapping applications, Differential

Correction is performed in the office using GPS

post-processing software.

• Real - time Differential Correction

For navigation and other applications which require

“in-field” accuracies, GPS receiver can be equipped to

receive a real-time corrected signal.

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Differential CorrectionPost-processing Requirements

• GPS receiver (rover) data

• Post-processing software

• Access to Base Station data

• Base station data must cover the exact same time period as GPS rover data.

• Base station must have tracked the same satellites rover tracked.

A Base Station is a GPS receiver logging data at a known location

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A final, differentially corrected position for the field data. [5 M (2 DRMS) or better]

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Removing Error with Post-Processing DifferentialBase Station Rover

The software looks at the uncorrected rover position [100 M (2 RMS)] and then...

You take a position fix in the field with GPS.

[100 M (2DRMS)]

At the same instant, a GPS base station also calculates its position.

The software calculates a correction factor (3) based on the known base station position (3A) and the GPS calculated base station position (3B).

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2

3

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Computes the rover data based on the correction factor that was determined in Step 3 which gives ...

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2

3

3A

3B

5

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Large distance betweenbase station and rover

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Before and After DifferentialBefore

• Uncorrected GPS positions have 50 - 100 Meters of error

• Each uncorrected position is represented by a yellow node

• Corrected GPS positions have up to 5 meters of error*

• Each corrected position is represented by a blue node

* Note: Not all positions in a job may be corrected by differential.Error after correction varies according to receiver qualities, GPS conditions & positioning method.

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After

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Real-Time Correction MethodsC/A Code

• Real-Time allows you to receive a corrected position in the field.

• Accuracy is about the same as the post-processed accuracy for a given unit.

• Several real-time methods are available: - Coast-Guard Beacon Receiver Many areas in US covered; use beacon receiver to get real-time corrections

- Radio-Modem broadcast Setup your own base station and broadcast RTCM signal

- Third-Party Sources

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GPS unit with beacon or RTCM receiver

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Real-Time Correction Example• GPS unit tracks satellites to get position

• RTCM receiver picks up a “corrected” signal

• Correction is applied to position to determine a real-time corrected position

Coast Guard Beacon Tower or Radio-Modem Transponder

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GPS/GIS Data Collection Concepts

- What are Features, Attributes, & Values?

- Feature Types: Points, Lines, Areas

- Data collection modes: Static & Dynamic

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Feature- An Object - (Point, Line or Area)Tree, Stream, Timber Stand, etc...

Attribute- Information about the Object (The Question)Species, Age, Height, etc...

Value- The Answer to the Attribute QuestionDouglas Fir, Ponderosa Pine, Ash, etc...

Features, Attributes, ValuesDescribing the objects you Map

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Feature RecordsGIS data and GPS positions

LAT: 44 32 45.5611N LON: 123 14 22.1661W HAE: 63.5 Meters

Tree, Species: Fir, Stand No: 1

• The GPS/GIS unit stores “Feature records”.

• A Feature record includes: - Feature positions (X,Y,Z) - Feature name - Attribute/Value Description

A Feature record may contain numerous Attributes and Values. A GPS Job may contain hundreds of Feature records.

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What is a Feature List?

• A “list” of the Features, Attributes and Values you wish to collect in the field.

• Feature List can be created in PC-GPS or on the GPS unit.

• Structure of Features, Attributes, Values can be tailored to match your GIS or mapping objectives.

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Features Attributes Values

Tree Species Douglas Fir

Ponderosa

Oak

Ash

Feature List organization

Each Feature in the list may have many Attributes & Values.Copyright CMT, Inc.

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Feature Types

There are three Feature Types:

Points: tree, hydrant, soil sample

Lines: road, stream, gas line

Areas: timber stand, crop field

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GPS collection of a Point

Point Feature:

- A number of GPS fixes (X, Y, Z) are averaged to calculate a position.

- The number of GPS fixes is set by the “session time” in the Feature List.

- Session time is in seconds and the GPS unit will store 1 GPS fix per second.

For C/A Code, session time might range between 20 seconds and 180 seconds.

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GPS collection of a Point

• GPS user goes to Point Feature and “stores” the point. [F4] to Store.

• GPS unit records a position fix each second. For a session time of 60, GPS unit stores 60 fixes (XYZ positions).

• Fixes are automatically averaged to calculate Feature position.

Tree Feature

60 Fixes - individual XYZ positions

LAT: 44 32 45.5611 N LON: 123 14 22.1661 WHAE: 63.5 MetersCopyright CMT, Inc.

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Different Types of Points

• “Standard” Point- You are able to place the GPS receiver at the exact location of the

Point.

• “Offset” Point- You are not able to place the GPS receiver at the exact

location of the Point. The location of the Point is calculated

based on Distance, Azimuth & slope from GPS receiver.

• “Nested” Point- The Point you want to store is near the Line or Area Feature that

you are currently storing. You can store the Nested Point without ending your Line or Area.

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Offset & Nested Point

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Offset Point Example:

40 FeetAzimuth = 290Slope = 0

occupy position Store offset Point

Feature position

• Use OFFSET [F3] before you store the Point.

• Input the Distance, Azimuth, Slope between occupied position and Feature.

• STORE offset information & then STORE Feature position.

Note: offset can be manually entered or automatically

“shot” with laser range finder. Nested Point Example:

Storing Line

Store Point

Continue Storing Line

• When storing Line or Area, stop and use PNT [F2]. The Line/Area will be paused.

• Go to the Feature position and STORE the Point.

• Return to Line/Area and CONT [F1] logging.

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GPS collection of a Line or Area

Line or Area Feature:

- A number of GPS position fixes (X, Y, Z) are “connected” to follow course of the Line or the boundary of the Area.

- The “interval” set in the Feature List determines how often a GPS fix is taken.

- Interval is in seconds. An interval of 1 means a fix will be taken each second.

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GPS collection of a Line

• GPS user walks or drives along road. GPS unit stores position fixes based on Interval.

• Lower interval provides more “definition” at a similiar rate of speed.

1 second

5 second10 fixes

10 second5 fixes

Example - User stored 75 meters at different intervals:

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50 fixes - each blue square is a position fix

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GPS Feature Collection Modes

• There are two collection modes:

- Dynamic mode

- Static mode

• Point Features are always Static.

• Lines & Areas can be Dynamic or Static.

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Static mode vs. Dynamic mode

• Dynamic mode assumes the GPS receiver is in motion while collecting data

• Static mode assumes the GPS receiver is stationary while it collects data

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Your job can be collected in LLA, UTM, SPC or a User system. The coordinate system or datum of the job can also be converted after download.

1. Select the Map/Coordinate System menu option.

2. Choose the Coordinate System, Datum, Zone and Unit of Measure.

3. Click on the OK button.

Coordinate System & Datum Conversion

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Importing Data & Combining Job Files

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Hints for Importing:

• You need to know the exact Coordinate System, Datum & unit of measure for the data you are importing.

• Coordinate System, Datum and/or Unit of imported file will be converted to match the “destination” file.

Import Formats

Import Steps:1. Choose Format

2. Click on Import Icon

3. Choose Files

4. Specify Coordinate System, Datum and Unit

5. Click on OK button

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Aerial Photos, Geo-Tiff, Digital Camera• Import Geo-Tiff images - Digital Raster Graphics, Digital Ortho Quad in TIF/TFW (ArcView) format

• Import Unreferenced Images in TIF, JPG, BMP formats

• For unreferenced images, use Control Points to Georeference

Hints for “Heads-Up” digiziting:

• Create a new Topic using Topic/New Topic

• Make Topic active & use Map/Add Features/By Mouse

Import Geo-Tiff Image

1. Use Map/Georeference Image or Icon

2. Select Image file from Open dialog.

3. Specify Coordinate System, Datum, Unit

Result: Image will be displayed

Images in your Map

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Viewing Photo Later: • Select Feature and then use View/Photo function.

• Double-click on Feature and then use the Photo button.

Tie Photo to a Feature

1. Double-click on the Feature.

2. Click on the Photo button in the Feature Update screen.

3. Click on the Select Photo button.

4. Choose Select from File.

5. Select a photo file (JPG, TIF, BMP).

6. Click on OK.

Digital Camera Photos can be added to your Map• Photos in a JPG, TIF, or BMP format can be added to your Map.

• PC-GPS can also download photos directly from a Kodak digital camera.

• Photos of a specific Feature can be displayed with a mouse-click.

Using Digital Inspection

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