NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Deviation Card with GPS
From: hellos
Date: 2006 Jul 25, 16:51 -0500
Bill-
Do you remember the days of LORAN C?
Most units had a dampening/averaging factor that was user selectable, i.e. to
average data and present a display based on the last 10-20-30 seconds, etc.
Consumer GPSes do not, as far as I know, have any similar option. They simply
perform internal calculations and, if you are lucky, they present "the latest"
data once per second on the NMEA output bus and the screen. If a vendor chose to
take longer to average data (like course headings) or used slower cheaper
hardware that was really using a longer time base to present this information,
there's no way you would know about it.
So I'd suggest that part of the problem is that both the GPS "heading" and the
mag compass heading are dynamic displays, and you can't expect them to compare
until you can freeze both and be sure they are effectively static. With the
antenna on the boat swinging around...sure, that will be a problem.<G> Compass
card is swinging too, the twain will probably never meet.
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From: hellos
Date: 2006 Jul 25, 16:51 -0500
Bill-
Do you remember the days of LORAN C?
Most units had a dampening/averaging factor that was user selectable, i.e. to
average data and present a display based on the last 10-20-30 seconds, etc.
Consumer GPSes do not, as far as I know, have any similar option. They simply
perform internal calculations and, if you are lucky, they present "the latest"
data once per second on the NMEA output bus and the screen. If a vendor chose to
take longer to average data (like course headings) or used slower cheaper
hardware that was really using a longer time base to present this information,
there's no way you would know about it.
So I'd suggest that part of the problem is that both the GPS "heading" and the
mag compass heading are dynamic displays, and you can't expect them to compare
until you can freeze both and be sure they are effectively static. With the
antenna on the boat swinging around...sure, that will be a problem.<G> Compass
card is swinging too, the twain will probably never meet.
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---
