GPS 4 GIS

Joel Cusick

National Park ServiceAlaska 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

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

• 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

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

Tablet Earth

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

Waypoint1N 61 13 9.0W 149 53 28.4

A GPS Line or TracklogA GPS Line or Tracklog

Start

Distance is the logging rate

= Vertices

Collecting Points or Waypoints along the Way

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 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

• 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 = 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

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",6378137,298.257222101]],PRIMEM["Greenwich” ,0],UNIT["Degree",0.0174532925199433]]

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