Tools of the Trade GPS Communication Software GPS Mapping ProgramTarpits and Tips

Tools of the Trade - Part IV Tarpits and Tips

Outline Datums Error, Accuracy, and Precision Map Scale and Errors Tips for Managing GPS Error Better Maps for GPS

GPS Datum Tarpit What’s the big deal –A football field of difference if you are wrong! –Ask the 3 soldiers in Afghanistan

Datum Shift 90 feet Florida Example If you were in Alaska

GPS Datum Tarpit –Summary: Know your Datum at all times When you hear WGS84, it’s the same as NAD83 Aviation GPS is always WGS84

Error, Accuracy, and Precision Importance –Safety –Make or break a GIS project Learn ways to keep GPS errors to a minimum Be aware of the issues Kenneth E. Foote and Donald J. Huebner, The Geographer's Craft Project, Department of Geography, The University of Colorado at Boulder.

1.) Accuracy: how close to truth or accepted values. 2) Precision: how repeatable or consistent Basic Definitions

3.) Error: includes both the imprecision of data and its inaccuracies Basic Definitions = Low Error !Accurate + Precise

False Advertising Beware of False Accuracy and False Precision –UTM = 1 meter –DMS.S = Translates to about 3 meters

Map Scale Accuracy and Precision for a map are a function of the scale at which the map was created Applies for digital or paper National Mapping Accuracy Standards employed by USGS

Accuracy Standards for Various Map Scales 1:2,400 ± 6.67 feet 1:24,000 ± feet 1:63,360 ± feet 1:100,000 ± feet

Map Scale 1:12,000 R=33.33’ 1:24,000 R=40’ 1:2,400 R=6.67’

Map Scale - Points

Map Scale - Lines

Map Scale and the Garmin Question? Will your Garmin III Plus meet Mapping Accuracy standards for a 1:24,000 scale product? How about a 1:63,360? Today, we will answer that question?

Sources of Map Errors Age of Data Map Scale Digitizing Errors Mapsource data is 1:100,000 scale

Tips for Managing GPS Error Record Metadata: –Who, What, Why

Managing GPS Error Try to average points

Managing GPS Error Try to use Antenna when possible

Make Better Maps for GPS Basic Premise: –Maps and GPS are made for each other –Location finding requires map grids, labeled tics and graticules Ingredients Required: –ArcView –Coordinate Grid Maker extension* –Map Data *Christoph Feldkotter Version Available from

Importance of Datums How error free are you? By managing error you can beat the odds Summary