On Tue, 29 Jan 2008 05:35:59 -0800 (PST), GeoffSchultz
wrote:

It isn't clear where the video was shot, but if the video was shot
while at anchor, then you can easily understand why the radar overlay
of the charts isn't in sync as the GPS can't determine the course
while not in motion.

What is really needed is a separate fluxgate compass heading sensor so
that the chartplotter/radar does not depend on the GPS for directional
information (Course Over Ground/COG). COG can introduce heading error
even when the boat is moving if you are in a cross current or making
significant leeway.

http://www.jmsonline.net/RAYMARINE-S...DER-E12102.htm

or something similar.