I have finally figured out how to locate the precise coordinates on various markers in any area in the US. Today I used one to make a quick test of the accuracy of my Magellan SporTrak GPSr. GPSr = GPS receiver. The details of my test follow: The location of the marker was accurately, 42 26.583 N by 92 25.240 W at an altitude of 872 feet. I took four readings, one reading right on to begin with, then three others by walking away in three different directions, pausing a few seconds each time, then coming back to the marker and waiting for my Magellan SporTrak to average 30 times (30 seconds) each before recording a mark. I held my unit 5 feet above the marker (above the weeds). My averaged reading was 42 26.586 by 92 25.239 at an altitude of 875 feet: minus the 5 feet above the marker this = 870 feet. My unit was reading a WAAS satellite and was receiving 8 strong signals at the time. The area was wide open with no significant obstructions. There were fewer satellites in the N than any other area. 42 26.583 - true value 42 26.586 - my averaged value error = 0.003 minutes = 0.18 second too far N 92 25.240 - true value 92 25.239 - my averaged value error = 0.001 minute = 0.06 second too far E, NOT BAD!!!! According to http://jan.ucc.nau.edu/~cvm/latlongdist.html#formats the position error overall was 19 feet (mostly in latitude) at this latitude. 872 feet alt - true value 870 feet alt - my averaged value error = -2 feet, NOT BAD!!!! My actual readings ended with the following minutes: Lat (actual = 26.583) 26.584 26.589 26.584 26.586 Long (actual = 25.240) 25.240 25.239 25.238 25.238 Feet Alt (actual = 872 feet) 869 886 876 868 As one can see, it seems like the first reading I made was the most accurate one. I have the details about how a person may obtain the information needed to locate suitable markers [[in the US]] to test their own GPSr. Feel free to contact me if you want a copy of my instructions. Tom Iowa USA + + + ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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