﻿ Compare the Accuracy Between Different GPS Devices
Compare the Accuracy Between Different GPS Devices
Julian T. Rubin

 Regretfully, our two dogs (Kelly and Jojo) died in 2007 and 2015 respectively and we buried them a few meters apart. We recorded the coordinates of the graves at burial time using different GPS devices since eight years separated these two sad events. The distance between the two graves was no more than 20 m and when we tried, out of curiosity, to find out the distance between the graves according to the readings of the two GPS devices, at the two occasions, using an online Coordinate Distance Calculator, the result was a disappointing 1580 m – far beyond any reasonable excuse. And no wonder, the first reading was taken in 2007 probably with a simple device whereas the second reading was taken in 2015 using a more modern application (but still simple). But we could not be sure that the newer means also the better. To solve the mystery it is recommended, in similar cases, to use a third certified professional device in order to come to conclusions – which one, of the two, is the more accurate. This experience gave me an idea for an interesting science fair project – to compare the coordinate readings of different Smartphone GPS applications for finding out the most accurate. The comparison could be done relatively to some known monument like the Eiffel Tower or the Statue of Liberty, etc., whose official accurate coordinate information could be easily obtained from Wikipedia. On the way, elementary students can exercise methods of coordinate representation - the conversion of decimal degrees (DD) to degrees, minutes, and seconds (DMS) and vice versa. Middle or high school students can try to calculate the distances themselves without using an online coordinate distance calculator. The opportunity presented itself when we visited the East Coast (August 2015) and took coordinate readings at two tempting sites by two different GPS applications – Ground Zero (World Trade Center) and Statue of Liberty – and calculated the distance for each application, using online software, from the official coordinate point and compared. You can also try to calculate the distance between the two sites according to the coordinate readings of each application and compare to the distance obtained through Google Maps.

 Location Official Coordinates App A Distance App B Distance World Trade Center N 40.7117 W -74.0125 N 40.711986 W -74.013526 92 m N 40.711998611 W -74.013593888 98 m Statue of Liberty N 40.6892 W -74.0444 N 40.68981 W -74.046232 170 m N 40.689805 W -74.046297222 170 m

 To sum it up. Both applications have the same accuracy since 6 m of difference falls between the limits of civilian GPS accuracy standards. The discrepancy between the official readings and our applications' readings is only normal since the two sets were not taken from the same place, of course.

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