GPS 4 GIS Joel Cusick National Park Service Alaska Support Office Garmin Trimble PLGR Tips, Tricks and Tarpits Pro XR GeoExplorer 3

Dictionary of Terms How GPS Collects Data Overview of Main GPS Receiver Types The Right Tool for the Job Tarpits Outline

You collect or receive GPS data collected in Alaska You try to minimize positional errors along the way Ultimate goal is a GIS dataset Assumptions

Global Positioning Systems (GPS) Differential GPS –Real-Time Differential GPS –Post-Process Differential GPS How GPS collects Features in the Field Dictionary of Terms

Tracking a GPS Satellite Vehicle (SV) 28 Satellites Distance = 12,0000 miles Speed = 6000 mph GPS Space Segment

Mapping Grade Receivers Recreational Grade Receivers GPS Ground Segment Garmin Trimble Pro XR GeoExplorer 3

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 Dictionary of Terms Garmin

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

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

GPS View of the World Dictionary of Terms How a digitizing tablet is used today

Digitizing Terms Dictionary of Terms TabletEarth Traditional Way GPS Way Puck Nodes / Vertices GRAIN or WEED {*| DEFAULT | distance} GPS Antenna Positions Logging Rate

–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 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” Dictionary of Terms

Line and Point Features Waypoint1 N W

A GPS Line or Tracklog Start Distance is the logging rate = Vertices

Collecting Points or Waypoints along the Way Multiple positions averaged into a point

Hardware Software 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 What a GPS Mapping Receiver Should Do Tip: A Pause button is crucial to creating clean line/poly data in the field

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) What a GPS Mapping Receiver Should Do

Recreational Grade GPS - Garmin Mapping Grade GPS - Trimble Y-Code Receivers - Rockwell PLGR+96 GPS/GIS Field Mapping Tools Overview of Main Types Nerd Factor

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) Recreational Grade GPS - Garmin Garmin

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 Mapping Grade GPS - Trimble Trimble

Features Include: –Accuracy: Autonomous < 15meters 68% –Club Fed Only –Good under Canopy Y-Code Receivers - PLGR+96 PLGR

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) GIS/GPS Field Mapping Tools Garmin and IPAQ running ArcPad

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 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) 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) 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 GPS for GIS - Pros and Cons

GIS/GPS Field Mapping Tools Pros 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

Sorry… It’s a Multi - Tool Environment –Garmin –Trimble –…..PLGR Need to learn enough about each system to know when to use the tool 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) 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) 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 Right Tool for the Right Job

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? What is Best?

Cleaning the data Datums When to Hang it up TARPITS

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

GPS Datum Tarpit What’s the big deal –Differences: WGS84(NAD83) to NADCON Alaska 27 = meters 3parameter NAD27 to NADCON Alaska 27 = meters –#1 - KNOW the Datum –Accept that 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

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

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", , ]],PRIMEM["Greenwich”,0],UNIT["Degree", ]]

GPS Data Tarpits Data Dictionaries –Practice runs before the big day….then don’t change in middle of job –Keep it simple. Less is more

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

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