negative elevation? (GPS question) - Page 2 - ClubTread Community

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post #16 of (permalink) Old 05-29-2008, 08:24 AM
Scaling New Heights
Join Date: Apr 2007
Location: Hinton, Alberta, .
Interest: Geocaching Hiking Hunting
Posts: 74

More on datums at

quote:Translations among the various datums can be a cause of some errors. Garmin used the the Molodensky transform parameters for those datums and performs transformations as needed. This is a simplified model and can result in errors on the order of 10 meters in some cases. With this transform the WGS-84 and NAD-83 numbers are always the same while a better translation will show a slight difference in these two datums. For most of the US this difference is less than a meter rising to about 2 meters on the west coast. Still less difference than the accuracy of the unit in most cases. Modeling something as complicated as the earth does not lend itself to mathematical transformations so to achieve accurate results some information is contained in tables with model information used to access the entry in the table which is then interpolated to get the answer. It is not known where Garmin depends on models alone and where they supplement with tables.
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