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GPS 4 GIS. Tips, Tricks and Tarpits. Garmin. Pro XR. GeoExplorer 3. Trimble. Joel Cusick National Park Service Alaska Support Office. PLGR. Outline. Dictionary of Terms How GPS Collects Data Overview of Main GPS Receiver Types The Right Tool for the Job Tarpits. Assumptions.

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GPS 4 GIS

Tips, Tricks and Tarpits

Garmin

Pro XR

GeoExplorer 3

Trimble

Joel Cusick

National Park ServiceAlaska Support Office

PLGR


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Outline

  • Dictionary of Terms

  • How GPS Collects Data

  • Overview of Main GPS Receiver Types

  • The Right Tool for the Job

  • Tarpits


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Assumptions

  • You collect or receive GPS data collected in Alaska

  • You try to minimize positional errors along the way

  • Ultimate goal is a GIS dataset


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Dictionary of Terms

  • Global Positioning Systems (GPS)

  • Differential GPS

    • Real-Time Differential GPS

    • Post-Process Differential GPS

  • How GPS collects Features in the Field


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GPS Space Segment

  • Tracking a GPS Satellite Vehicle (SV)

  • 28 Satellites

  • Distance = 12,0000 miles

  • Speed = 6000 mph

http://liftoff.msfc.nasa.gov/realtime/jtrack/3d/JTrack3d.html


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Garmin

Pro XR

GeoExplorer 3

Trimble

GPS Ground Segment

  • Mapping Grade Receivers

  • Recreational Grade Receivers


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Garmin

Dictionary of Terms

  • GPS

    • Not for navigation anymore

    • Since Selective Availability SA was turned off…..

    • $300 unit can map at 1:24,000 scale (+/- 12m)

      • in the open

      • but not under canopy

http://www.fs.fed.us/database/gps/


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Dictionary of Terms

  • Differential Global Positioning System (DGPS)

    • Any system that can remove atmospheric errors in a GPS solution (greatest error after SA)

      • Realtime

      • or back in the office - Post-Process


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Dictionary of Terms

  • Real Time Differential GPS

    • CORS BASE Stations

    • In Alaska - depends on where you are at and how lucky you are

    • Dependent on the CORS Network - Gulf of Alaska:

      • Hit / Miss

      • Not dependable


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Dictionary of Terms

  • Real Time Differential GPS

    • WAAS

      • Wide Area Augmentation System

      • Designed for high flying aircraft

      • 2 Geostationary satellites (parked over equator)

      • 3 meter solution (if the GPS is enabled)

      • Hit / Miss in AK

      • Poor under any canopy

Tip: Other Satellite DGPS systems like StarLink do not cover AK


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Dictionary of Terms

  • Post-Process Differential GPS

    • Dependent on the CORS Statewide Network and community base stations

      • Increasing coverage

        • Prudhoe Bay on line

        • Kotzebue soon?

      • Baselines have significantly decreased

Tip: For every 100km between base and rover, add additional 0.1m of error


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Dictionary of Terms

  • GPS View of the World

How a digitizing tablet is used today


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Dictionary of Terms

  • Digitizing Terms

Traditional Way GPS Way

Tablet

Earth

Puck

GPS Antenna

Nodes / Vertices

Positions

GRAIN or WEED {*| DEFAULT | distance}

Logging Rate


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Dictionary of Terms

  • A GPS View of GIS Features

    • Point features are one or more positions averaged into a point

      • Mapping Grade Receivers : Called “Points”

      • Recreational Grade Receivers : Called “Waypoints”

  • String of positions converted into a line / area

    • Mapping Grade Receivers : Collected directly in the field as a line / area feature

    • Recreational Grade Receivers : Collected as a “TrackLog” then converted back in the office


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Waypoint1

N 61 13 9.0

W 149 53 28.4

Line and Point Features


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Distance is the logging rate

A GPS Line or Tracklog

= Vertices

Start


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Collecting Points or Waypoints along the Way

Multiple positions averaged into a point



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What a GPS Mapping Receiver Should Do

  • Hardware

    • Accuracy (How close to Truth)

      • Meet National Mapping Accuracy Standards:

        • 1:63,360 (32meters)

        • 1:24,000 (12 meters)

        • 1:5,000 (4 meters)

    • Precise (How reliable)

    • Rugged

    • Able to Average Positions into a Point

    • External Antenna Options

    • Good on Batteries

No Problem!

Most Likely

With Effort

Tip: A Pause button is crucial to creating clean line/poly data in the field


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What a GPS Mapping Receiver Should Do

  • Software

    • Export in GIS Friendly Formats (shapes, coverages, DXF)

    • Capable of Controlling Attributes in the Field

      • Data Dictionary (Name, Trail Width, Comments)

    • Capable of Datum Transform - To NADCON 27

    • Mission Planning

      • Sky Plots

      • Planning the day

    • Able to Differentially Correct (Realtime or Post-process)


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Overview of Main Types

  • Recreational Grade GPS - Garmin

  • Mapping Grade GPS - Trimble

  • Y-Code Receivers - Rockwell PLGR+96

  • GPS/GIS Field Mapping Tools

Nerd Factor


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Recreational Grade GPS - Garmin

  • Features Include:

    • Accuracy:

      • Autonomous < 15meters 68%

      • DGPS ready 1-5 meters 68%

    • User Friendly

    • Many models

      • Garmin GPSIII+, GPSMap76, eTrex

    • Moving Base Maps (1:100,000 scale)

Garmin

RealTime Kit


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Mapping Grade GPS - Trimble

  • Features Include:

    • Accuracy:

      • Autonomous < 15meters 68%

      • Post-Process DGPS

        • 3-5 meters 95% (Geo3)

        • 1 meter 95% (ProXR)

    • Pathfinder Office Software

      • Data Dictionary, Mission Planning

Trimble


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Y-Code Receivers - PLGR+96

  • Features Include:

    • Accuracy:

      • Autonomous < 15meters 68%

    • Club Fed Only

    • Good under Canopy

PLGR


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GIS/GPS Field Mapping Tools

  • GPS unit + Handheld PC(CE) + ArcPad:

    • Realtime display of vector /raster data

    • Hook to any GPS

    • Unlimited Storage (dependent on storage capacity of device)

    • Instant shapefile creation

    • Application builder($1500)

Garmin and IPAQ running ArcPad


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GPS for GIS - Pros and Cons

  • Garmin III+

    • Pros

      • Cheap and consistent 15 meters positions - okay under canopy

      • Good “Point tool”

      • Fun / easy to use and easy to navigate with

      • Integration into ArcView - relatively straightforward

      • Battery usage is great

    • Cons

      • Cheap

      • No GPS Filters (2D Fixes Given, SNR, PDOP, MASK Angle set to 5)

      • Position accuracy not recorded

      • Not designed for GIS Mapping - relies on 3rd party software

      • No Data Dictionary capability

Large Errors!


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GPS for GIS - Pros and Cons

  • Trimble GeoExplorer 3

    • Pros

      • 2-5 meter mapping tool

      • Point/Line/Poly Tool

      • Rugged

      • Collect data for 16 hours

      • Exports in coverage or shapefile

      • Excellent software (Pathfinder Office)

    • Cons

      • Requires additional training

      • $4000

      • Under Canopy issues - Velocity filtering / Use Antenna

      • Need to post-process after the field (internet connection)


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GPS for GIS - Pros and Cons

  • Trimble Pro XR

    • Pros

      • Top-of-the-line GIS Mapping Tool

      • Submeter to 2 meter Tool

      • Real-time DGPS

      • Point/Line/Poly

      • Excellent under Canopy

      • Rugged

      • Exports in coverage or shapefile

      • Excellent software (Pathfinder Office)

    • Cons

      • Requires additional training

      • $8,000 - $10,000

      • Big/Bulky

      • Need to post-process after the field (internet connection)


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GPS for GIS - Pros and Cons

  • PLGR

    • Pros

      • Good “Point tool”

      • Records error and Datum

      • Integration into ArcView - relatively straightforward

    • Cons

      • Older technology - Phasing Out

      • Heavy

      • Does not store an AVERAGED solution

      • Terrible on batteries

      • Club Fed only

      • No Data Dictionary capability


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GIS/GPS Field Mapping ToolsPros and Cons

  • IPAQ / ArcPad

    • Pros

      • Now can select GPS Filters (SNR, PDOP)

      • Creation of shapefiles

      • Pen-based digitizing from the air

      • Measure distances in field

    • Cons

      • Not a tight package (GPS, cables, ipaq, cradle, software, data)

      • Small screen view

      • Purchase of ruggedized collectors($900 - $3000)

      • GIS skills support is high (design forms, maintain/move data)

      • Battery usage poor


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Right Tool for the Right Job

  • Sorry… It’s a Multi - Tool Environment

    • Garmin

    • Trimble

    • …..PLGR

  • Need to learn enough about each system to know when to use the tool


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Right Tool for the Right Job

  • Mapping Scenarios:

    • Garmin / PLGR

      • Mapping sheep from the air?

      • Record cabin (points) location for fire

      • Photo control for georeferencing an AHAP (1:60,000) photo

      • Mapping study sites; Inventory and Monitoring

    • Garmin\PLGR\Trimble

      • Mapping a trail from a fast moving vehicle or by air (moving)


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Right Tool for the Right Job

  • Mapping Scenarios cont:

    • IPAQ/ArcPad

      • Mapping fires from the air - need to know position now

      • ARC IMS connectivity to mothership???

    • Trimble

      • Mapping a Road while collecting point features along the way

      • Mapping a trash can lid

      • Mapping complex attributes?

      • Photo control for larger scale maps (1:12,000)

      • Updating of existing GIS layers

    • PLGR

      • In Dense Canopy (but prefer XR)


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Right Tool for the Right Job

  • Putting it another Way:

    • If accuracy is the key...

      • Map a SUV - Garmin or PLGR

      • Map a small Subaru - Garmin (Average) or Trimble

      • Map a bunch of scooters - Trimble and post process

      • Map the four corners of an archeology dig (10 meters across)

        • Pull out the Survey equipment

    • If mapping features is the key...

      • Map a trail network - limited funds, inexperienced personnel - Garmins

      • Map a campground - tentpads, sign posts- Trimble


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What is Best?

  • Ask Yourself

  • 1) What are your accuracy needs?

    • A) resolution of the other data types

    • B) anticipated data for the future

  • 2) Project Needs

    • A) What are the crews GIS skills

    • B) Is it just you dealing with the data

  • 3) What part of Alaska are you working in?

  • 4) How much money do you have?


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TARPITS

  • Cleaning the data

  • Datums

  • When to Hang it up


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QC / Clean Tarpit

  • Coverages

    • Set Precision to Double Double

    • Check out the data tolerances first -measure distances between vertices

    • Watch for places where a GPS was left on and dropped a bunch of vertices


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GPS Datum Tarpit

  • What’s the big deal

    • Differences:

      • WGS84(NAD83) to NADCON Alaska 27 = 100-150meters

      • 3parameter NAD27 to NADCON Alaska 27 = 1.5 - 8 meters

    • #1 - KNOW the Datum

    • Accept that 1.5 - 7 meters might not be a big deal

      • Depending on the GPS, method of acquisition, scale of base data etc.

    • In your mind, switch WGS84 with NAD83


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GPS Datum Tarpit

  • How to deal with it

    • Ask? Demand the Datum be written down

    • Know how the Data arrives to the PC

      • Garmin - Garmin Protocol - WGS84(NAD83)

      • Garmin - via NMEA - up to the Display

    • If a Trimble

      • Handle datum in Software - FOR NAD27 EXPORTS ! USE NADCON27 ALASKA

Airplane GPS is always WGS84


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Datum Solutions

  • Use prj files to eliminate the define projection step

    • Keep a set of NAD83 and NAD27 prj files around

    • Copy the prj alongside the *.dbf, *.shx, *.shp

GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137,298.257222101]],PRIMEM["Greenwich” ,0],UNIT["Degree",0.0174532925199433]]


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GPS Data Tarpits

  • When to “Hang it Up”

    • Effective GPS for GIS purposes requires

      • In Super thick canopy or canyons?????

      • Attentive field personnel (“A Field Nerd”)

    • Mapping may be more efficient by..

      • remote sensing

      • heads-up digitizing


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Summary

  • GPS not for navigation alone

  • Rapidly evolving technology - Migration to Windows CE and mult-tasking environments

  • GPS Toolbox may require several tools to get the job done

  • Instead of waiting for an updated Map product do it yourself and enjoy the outdoors


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