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PCCC GIS I Exercise 2 (AV9.1) - Locate your car with GPS, map it with GIS v2, Apr 2007 - page 7 / 31





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southeast. This correction is applied to each of the rover’s 100 points, then averages all of those positions together and reports a position with some confidence interval, such as +/- 1 foot. There may still be some uncertainty in the GPS position, but it will be far more accurate than the

uncorrected position. Perhaps the “zone of uncertainty” now looks like a small circle with a

radius of 1meter

rather than a heaping pile of spaghetti.

Procedure: From the PFO menu, Go to

Utilities > Differential Correction > Internet Search There are a number of base stations available from which you can download the differential correction information that will correspond to the hour(s) in which your data were collected. I have had good luck with the CORS station in Trenton, NJ. Once you have selected the base station file you wish to use, press OK. Some blue bars whiz by, and you are done with the correction.

Go to C:pfdata\default and you will note a difference in the icons for data, even though the file names are the same. The differentially corrected data files can be identified with little blue/red bullseye icons, and they will also have a .cor (for “corrected”) suffix appended to their file names.

Step 5 - Use PFO to export differentially-corrected data from GPS to GIS format Discussion: You are now at the point where you will convert the GPS data to Arcview shapefile format, then export it. Prior to export, you can select the coordinate system of your differentially corrected data so that it will match that in your GIS view.

Procedure: Set up a new folder on the GIS server, inside the current semester’s GIS_I folder. Name this new folder group_ *_GPS (where * = your group number). If you are working alone, place this folder inside your own GIS Exr02 folder.

  • From the GPS PFO main window, select Utilities > Export.

  • The Export window appears:


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