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

Mapping Program

Tarpits and Tips

Tools of the Trade

GPS


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

  • What’s the big deal?

    • A football field of difference if you are wrong!

    • What if you’re on the wrong side of the ridge?

    • Or worse…the valley!!

SHIFT HAPPENS!


Datum Shift

0.13miles

Shift Happens - Florida Example


Shift Happens - Redmond OR 2005 Example

710 Feet


In the Field

Comms between GPS users

Comms between GPS and Maps

Example: dispatch in one datum, you read off in another

In the GIS

Projecting data on top of GIS data

Example: You set DNRGarmin Projection to UTM 10 NAD83, but your GIS is in UTM 10 NAD27

When Datums Matter


Written

or Spoken

Datum MISMATCH

Them

You

400 feet off

Display set to NAD27

They Expect WGS84


Transfer to

GIS

Set Projection in DNR Garmin to NAD27

GIS

GPS

Always Stores in WGS84

Working in NAD27


GPS Datum Tips

  • Summary:

    • Check, check, check

    • When Downloading with DNR Garmin, Always check “Set Projection” to match your GIS

    • ASK!

    • When you hear WGS84, with your scale, 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.


Basic Definitions

1.) Accuracy: how close to truth or accepted values.

2) Precision: how repeatable or consistent


Basic Definitions

Accurate + Precise

= Low Error !

3.) Error: includes both the imprecision of data and its inaccuracies


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


Map Accuracy Standards

  • 1:2,400 ± 6.67 feet

  • 1:24,000 ± 40.00 feet

  • 1:63,360 ± 105.60 feet

  • 1:100,000 ± 166.67 feet


Map Scale and the Garmin

  • Will your Garmin GPS MAP76 meet Mapping Accuracy standards for a 1:24,000 scale product (+/- 40’)?

  • How about 1:63,360 (+/-105’)?

  • Yesterday, we answered that question?


Sources of Map Errors

  • Age of Data

  • Map Scale

Mapsource data is 1:100,000 scale

  • Digitizing Errors


Tips for Managing GPS Error

  • Metadata

  • Average all Points

  • Fresh batteries

  • External Antenna

  • All else fails

    • Map and Compass


Tips for Managing Error

  • Staying As Accurate as possible

+/-26 ' (open)


Tips for Managing GPS Error

  • Record Metadata:

    • Who, What, Why


Managing GPS Error

  • Try to average points

  • 60 points


Managing GPS Error

  • If in the trees, turn off WAAS

  • Position can be even worse.

  • Always take a 3D position over a 2D Differential!


Managing GPS Error

  • Try to use Antenna when possible

  • A Map76 under Canopy gets twice as accurate with an external antenna

  • Use Sleeve mounts if you have to

  • When mounting in vehicle, use brackets


GPS Accessories

  • Maps

  • Compass

  • GOTO:

    • Distance

    • Bearing


Ideal GPS Accessories

  • Extra AA batteries

  • Case ($14.00)*

holds cables,

cameras,

batteries

*Available www.gpsoutfitters.com


Make Great Maps

  • Practice Collecting Good Data in the field

  • Pass onto others only important stuff

  • Make your data secure


Future Firefighters


Summary

  • Importance of Datums

  • How error free are you?

  • By managing error you can beat the odds


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