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Elevation Determination using the Garmin 12XL GPS with Differential Correction

The following table will give some idea of the accuracy of the elevations measurements made by the differentially corrected Garmin 12XL GPS. The "Map" numbers come from the "Ohlone Wilderness Regional Trail Permit," available from the East Bay Regional Park District at Sunol Regional Wilderness and Lake Del Valle. Of course it's possible that the GPS measurement is more accurate than the numbers on the map, whose method of determination is not specified. All numbers are in feet for ease of comparison to the map. From each GPS measurement, I subtracted 3 feet to account for the height of the GPS above the ground level during the measurement.

Place Map Elevation GPS Elevation
Stanford Ave. staging area 390 394
Summit 2517 2504
Post 4, near privy 2030 2008
Post 7, Laurel Loop/Eagle Trail Junction 2090 2087
Post 8, Laurel Loop/Laurel Canyon Trail Junction West 2010 1995
Post 9, Laurel Loop/Laurel Canyon Trail Junction East 1840 1828
Post 11, near Calaveras Road 770 771
Post 12, Sunol Regional Wilderness sign-in board 390 379

One likely source of discrepancy is that in some places (e.g. Stanford Staging Area), it's not clear where precisely the "Map" measurement was made. Another is that the zero reference for the map is not specified; there are various algorithms for determining what the local sealevel reference should be.

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$Date: 2005/10/23 04:28:07 $ ..