Interestingly enough, GPS calculates speed through the Doppler shift effect when triangulating location. A ping from 3 different locations are sent out at regular intervals and the shift in relation to those 3 points is used to calculate speed.
Are you sure that cellphones and hand-held GPS's do that? I thought they just used position versus time.
I think I may know someone who can answer this comprehensively...I'll try to get the actual facts.
But it really doesn't matter. The end result is the same.
Radar analyzes a Doppler shift from a single point source. GPS analyzes Doppler shift from 3 different point sources. Radar is more minutely accurate on short distance changes in acceleration because the waveform is a much higher frequency.
The frequency variations don't matter with straight lines or wide turn radii. That's why I made the statement about a 747 turning in the same kind of radius as a human.
Thank you,
CriticalThinker
Where in the NMEA output is speed? What point sources?
I should have been a tad more specific. At least 3 point sources.
Example NMEA data:
$GPGGA,181908.00,3404.7041778,N,07044.3966270,
W,4
13,1.00,495.144,M,29.200,M,0.10,0000*40
13 would be the number of point sources. And it would be the delta in the 3404.70417 & 07044.3966270 that produce a Doppler shift effect for speed output. While the values are expressed in the format of lat/long. They are attained by a minimum of 3 signals for triangulation. As each point source sends and electromagnetic radio wave to the radio antenna of the unit for triangulation, the validity on a flat/round earth remains consistent. The waves come downward at an angle to the antenna instead of at ground level but the physics is the exact same as radar.
Thank you,
CriticalThinker