NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: sight reduction with GPS receiver
From: Brooke Clarke
Date: 2005 Mar 21, 18:24 -0800
From: Brooke Clarke
Date: 2005 Mar 21, 18:24 -0800
Hi Frank:
Most modern GPS receivers have built in a couple of dozen different models of the Earth. For example the North American Datum of 1927 (NAD27) is common for many maps of the U.S. and gives a better match than WGS84. Each country used it's own local model before a world wide model existed. There are also a number of DIFFERENT WGS84 models with a year suffix.
My house GPS antenna is at 39:11:24.5833 N, 123:09:50.4842 W, 920.14 feet WGS84.
Have Fun,
Brooke Clarke, N6GCE
Frank Reed wrote:
Most modern GPS receivers have built in a couple of dozen different models of the Earth. For example the North American Datum of 1927 (NAD27) is common for many maps of the U.S. and gives a better match than WGS84. Each country used it's own local model before a world wide model existed. There are also a number of DIFFERENT WGS84 models with a year suffix.
My house GPS antenna is at 39:11:24.5833 N, 123:09:50.4842 W, 920.14 feet WGS84.
Have Fun,
Brooke Clarke, N6GCE
-- w/Java http://www.PRC68.com w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml http://www.precisionclock.com
Frank Reed wrote:
Chas you wrote:"If anyone cares to try a different GPS
receiver, be certain it is set for WGS84
and directions are reported with respect
to true north."What other options can you specify besides WGS84? (the only GPS receiver I own is an early basic model with no bells and whistles)By the way, I should have thought of this earlier, there is a simple test for ellipsoidal versus spherical distances. Set the device to calculate the distance between Lat,Lon of 0,0 and 0,90 (both points on the equator). Then calculate the distance between Lat,Lon 0,0 and 90,0 (along the Greenwich meridian to the North Pole). If the calculation is spherical, the distances will be the same.