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: Herbert Prinz
Date: 2005 Mar 18, 19:16 -0500
From: Herbert Prinz
Date: 2005 Mar 18, 19:16 -0500
Paul Hirose has surely found the most sophisticated way of landing in the reefs with the combined assistance of GPS _and_ a sextant! A GPS receiver normally shows distance between two points along the geodesic. For the points in the given example the answer using WGS84 is 2229 nm, being 3 miles off the GCD. In a worst case scenario, (e.g. establishing latitude at N45 from the sun at winter solstice) the discrepancy is 20 miles! In order to use your GPS receiver as a makeshift sightreduction computer, you have to cajole it into using a spherical earth model. On some models this is not a trivial task - if possible at all. (To say nothing of the practical aspect of making sure that a GPS receiver that has been upset in such a fashion does not end up in the nav station by mistake, quasi as a time bomb ready to explode at the moment of landfall. But practical aspects hardly play any role in this discussion.) Herbert Prinz Paul Hirose wrote: >There are other ways a GPS receiver can assist with traditional >navigation. For example, let's try a sight reduction. >