1. Global Mapping Technology Products and Training for GPS/GIS/SURVEY
GMTGPS
1107 NW Oak Av Corvallis OR
Ph: Fax: 1 1

2. Global Mapping Technology Products and Services
GPS/GIS and GPS SURVEY PRODUCTS
GPS MAPPING SERVICES
GPS/GIS TRAINING
LASER RANGE FINDER MAPPING

3. The Global Positioning System
A Constellation of Navigation
Satellites Orbiting the Earth
GPS is operated and maintained by the
United States Department of Defense 4 4 4
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4. 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 5
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5. What is GIS? Geographic Information Systems
GIS allows us to create maps
GIS provides tools for analyzing geographic information 6
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6. 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 7
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7. GPS/GIS Applications Forestry/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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8. 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: N LON: W HAE: 63.5 Meters
Tree, Species: Fir, Stand No: 1,
2. Information from GPS/GIS unit is downloaded to a GPS/GIS program. 8 8
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9. Example of GPS/GIS collection (Step 3 and Step 4)
3. In the GPS/GIS program, differential correction may be performed to improve accuracy of GPS coordinates.
4. A finished map, complete with symbols and labels, is created.
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10. Specifics on GPS Technology
- GPS System Overview
- How GPS receiver calculates position
- How accurate is GPS
- What affects GPS accuracy 9
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11. The GPS system is comprised of three “segments”
GPS System Overview
The GPS system is comprised of three “segments”
Space Segment:
Control Segment:
User Segment:
GPS system was developed by the US Dept of Defense for military positioning applications. GPS is now widely used for civilian applications. 10 10 11
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12. Space & Control Segment
Satellites also called “SVs” or Space Vehicles
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 & clocks
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13. User Segment
“GPS receivers” are used in a variety of military and civilian applications.
GPS receivers track satellites and use SV signal information to calculate:
- position, velocity, time
The term “tracking satellites” means that the GPS unit is receiving radio signals being broadcast by satellites. 12
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14. How GPS Receiver calculates position
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.
All civilian-use GPS receivers track L1.
Some civilian-use GPS receivers can track L1 and L2. These receivers are referred to as “dual-frequency” receivers.
Difference between the two codes:
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. 10 17 10
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15. 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 SV, 2-D position will be computed. (XY) 11 11 18
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16. 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. 16
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17. 19 19 33
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18. 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. 20
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19. Differential Correction Post-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 21
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20. You take a position fix in the field with GPS. [100 M (2DRMS)]
Removing Error with Post-Processing Differential 1 2 3 3A 3B 5 6
Large distance between
base station and rover
Base Station
Rover
You take a position fix in the field with GPS. [100 M (2DRMS)] 1
At the same instant, a GPS base station also calculates its position. 2
The software calculates a correction factor (3) based on the known base station position (3A) and the GPS calculated base station position (3B). 3 4
The software looks at the uncorrected rover position [100 M (2 RMS)] and then... 5
A final, differentially corrected position for the field data. [5 M (2 DRMS) or better] 6
Computes the rover data based on the correction factor that was determined in Step 3 which gives ... 46 36 46
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21. Before and After Differential
Uncorrected GPS positions have Meters of error
Each uncorrected position is represented by a yellow node
After
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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22. Real-Time Correction Methods C/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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23. 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
GPS unit with beacon or RTCM receiver 18 11 11
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24. GPS/GIS Data Collection Concepts
- What are Features, Attributes, & Values?
- Feature Types: Points, Lines, Areas
- Data collection modes: Static & Dynamic 26
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25. Features, Attributes, Values
Describing the objects you Map
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 Question
Douglas Fir, Ponderosa Pine, Ash, etc... 27 27
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26. GIS data and GPS positions
Feature Records
GIS data and GPS positions
LAT: N LON: W 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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27. 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. 28
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28. Feature List organization
Each Feature in the list may have many Attributes & Values. 29 29
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29. Feature Types There are three Feature Types:
Points: tree, hydrant, soil sample
Lines: road, stream, gas line
Areas: timber stand, crop field 30
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30. 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. 31
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31. GPS collection of a Point
GPS user goes to Point Feature and “stores” the point. [F4] to Store.
Tree Feature
GPS unit records a position fix each second. For a session time of 60, GPS unit stores 60 fixes (XYZ positions).
60 Fixes - individual XYZ positions
Fixes are automatically averaged to calculate Feature position.
LAT: N
LON: W
HAE: 63.5 Meters 31
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32. 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. 32
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33. Offset & Nested Point Offset Point Example: Nested Point Example:
40 Feet Azimuth = 290 Slope = 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. 31
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34. 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. 33
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35. 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.
Example - User stored 75 meters at different intervals:
1 second
50 fixes - each blue square is a position fix
5 second
10 fixes
10 second
5 fixes 33
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36. 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. 34
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37. 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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38. Coordinate System & Datum Conversion
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.
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39. Importing Data & Combining Job Files
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
Import Formats
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.
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40. Aerial Photos, Geo-Tiff, Digital Camera
Images in your Map
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
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41. Using Digital Inspection
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.
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