NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Da Lurk
From: Jared Sherman
Date: 2003 Feb 9, 14:08 -0500
From: Jared Sherman
Date: 2003 Feb 9, 14:08 -0500
Fred-GPS knows nothing about steering directions, it only knows the actual course taken by the GPS antenna. If you are steering 340 but making 350 due to leeway, the GPS will only tell you that you are making 350. Or, that the GPS antenna is making 350 so it presumes the rest of the boat is moving that way too. GPS literally "can't" be swung like a compass can. GPS knows nothing about true/magnetic, unless someone tells it to display one versus the other and gives it deviation information. I'm not sure if that is available from the GPS system (I don't think so) but the deviation data for the world can be stored in ROM and then "generated" by the GPS unit running the current date against that to extrapolate the correct information for the time and position that the GPS system has given it. There was some discussion...here?...some time ago about one brand of GPS that indeed had a firmware error and was apparently calculating magnetic/true incorrectly. French or English I think--a brand that doesn't appear here on the US market.
