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Re: Horizontal Sextant angles plot.
From: Richard B. Langley
Date: 2012 Apr 6, 08:47 -0300
From: Richard B. Langley
Date: 2012 Apr 6, 08:47 -0300
GPS receivers determine their velocity vector from Doppler shift measurements not a succession of positions. Quoting from my article "The Magnetic Compass and GPS": "A GPS receiver can provide accurate information about its position and velocity, and from the velocity vector it can determine the direction in which it is moving - called the course or track. The accuracy with which a receiver can compute this direction depends on its speed (the velocity magnitude) but is usually better than one degree for speeds greater than about 10 kilometers per hour. The course is not necessarily the same as the heading or direction in which the GPS receiver, or the platform on which it is mounted, is pointing. A single-antenna GPS receiver cannot determine heading. However, a compass can provide this information and as mentioned earlier, some GPS receivers incorporate an electronic compass, usually a two-axis sensor. Some receivers have three-axis sensors that give relatively accurate bearings even if they are slightly tilted." The article can be found here: http://www.gpsworld.com/gps/the-magnetic-compass-and-gps-828 -- Richard Langley Quoting Alexandre E Eremenko: > > Lu, > >> The problem with "GPS as compass" is that GPSs can only determine position. >> Everything else that a GPS might show (especially direction of >> movement) is derived from a succession of positions. > > This was exactly what I thought when I was shown this "GPS compass". > One was supposed to turn the GPS device (like a compass) in certain > direction and it told you the asimuth of this direction... > with the error of sevral 10's of degrees:-) > > (I did not even need a compass to see this, an analog watch and the > Sun was enough). > > I imagine some people who believe in technology, carry only GPS > with them, and use this info without even looking at the Sun:-) > > Alex. > > > > ----------------------------------------------------------------------------- | Richard B. Langley E-mail: lang@unb.ca | | Geodetic Research Laboratory Web: http://www.unb.ca/GGE/ | | Dept. of Geodesy and Geomatics Engineering Phone: +1 506 453-5142 | | University of New Brunswick Fax: +1 506 453-4943 | | Fredericton, N.B., Canada E3B 5A3 | | Fredericton? Where's that? See: http://www.fredericton.ca/ | -----------------------------------------------------------------------------