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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Q: how to calculate refraction at higher altitudes on land?
From: Michael Wescott
Date: 2002 Feb 28, 14:55 -0500
From: Michael Wescott
Date: 2002 Feb 28, 14:55 -0500
> I am specifically trying to determine the elevation of my house.
>
> The topographic maps of my area are decades old. They do not show
> our streets or houses, and in fact the area has been graded to some
> extent as well, so even finding my exact location via GPS and then
> looking on the map only gives a ballpark figure.
>
> Since SA has been turned off, the GPS gives a range of elevations
> from 580 feet to 650 feet. The Garmin GPS 3 tends to wander over
> this range. I am trying to get a better value.
From what I have read, GPS height info has about twice the inaccuracy
as horizontal info. There is also the problem that heights, say on a
USGS map, are often referenced to Mean Sea Level and not a particular
ellipsoid. See http://www.ngs.noaa.gov/GEOID/GEOID99/ for more detail.
--
Mike Wescott
Wescott_Mike@EMC.COM
