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Tools of the Trade

GPS Communication Software GPS Mapping Program Tarpits and Tips Tarpits and Tips Tools of the Trade Tools of the Trade - Part IV Tarpits and Tips TIPS Outline Datums Error, Accuracy, and Precision Map Scale and Errors Tips for Managing GPS Error Better Maps for GPS GPS Datum Tarpit

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Tools of the Trade

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  1. GPS CommunicationSoftware GPS Mapping Program Tarpits and Tips Tarpits and Tips Tools of the Trade

  2. Tools of the Trade - Part IV Tarpits and Tips TIPS

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

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

  5. If you were in Alaska Datum Shift 90 feet Florida Example

  6. 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

  7. 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.

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

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

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

  11. 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

  12. Accuracy Standards for Various Map Scales • 1:2,400 ± 6.67 feet • 1:24,000 ± 40.00 feet • 1:63,360 ± 105.60 feet • 1:100,000 ± 166.67 feet

  13. 1:2,400 R=6.67’ 1:12,000 R=33.33’ 1:24,000 R=40’ Map Scale

  14. Map Scale - Points

  15. Map Scale - Lines

  16. 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?

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

  18. Tips for Managing GPS Error • Record Metadata: • Who, What, Why

  19. Managing GPS Error • Try to average points

  20. Managing GPS Error • Try to use Antenna when possible

  21. 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 2.270 Available from www.esri.com/arcscripts

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

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