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#1
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SeeYou question
Does anyone have any idea how SeeYou calculates the (ground) velocity at any
given fix in a flight? I'm examining the take-off segment of one of my log files, and when I calculate the velocity using the ubiquitous Great Circle algorithm from the previous fix to the current fix, I get velocities that are *much* higher than what SeeYou shows in the hover-hints as you trace the mouse along the route. Hack hack hack ~ted w/2NO |
#2
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A specific example:
In the log file in question, my take-off roll begins at 1:24:15pm, when the latitude/longitute fixes start to move. Calculating the instantaneous speed as the distance from the previous fix to the current fix divided by the time between those two fixes, I have these speeds: +15 seconds: 43mph +20 seconds: 59mph +25 seconds: 72mph +30 seconds: 81mph But loading the same file in SeeYou and looking at the data that pops up next to the mouse pointer and checking the speeds at the same points: +15 seconds: 13mph +20 seconds: 22mph +25 seconds: 33mph +30 seconds: 43mph Those are some rather drastic speed differences. The tow plane was one of Turf's Pawnees, which in the warmest weather don't have me sitting at 35 knots a full 30 seconds into the take-off roll. The distance algorithm I'm using is the classic Great Circle: distance_in_miles = 3956.0775034473 * arccos( SIN(lat1) * SIN(lat2) + COS(lat1)*COS(lat2) * COS(lng1-lng2) ) Any other hackers out there played with this stuff? -tw |
#4
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Hi Ted,
SeeYou uses a filter, a sort of smoothing algorythm for the groundspeed velocity calculations. Default value is 20s which means that 20 second. You can control the smoothing through Tools Options Statistics Groundspeed filter. Set it to "1s" to have "no filter". Regards, Andrej Kolar -- glider pilots use http://www.SeeYou.ws On Thu, 2 Sep 2004 22:10:58 -0700, Ted Wagner wrote: A specific example: In the log file in question, my take-off roll begins at 1:24:15pm, when the latitude/longitute fixes start to move. Calculating the instantaneous speed as the distance from the previous fix to the current fix divided by the time between those two fixes, I have these speeds: +15 seconds: 43mph +20 seconds: 59mph +25 seconds: 72mph +30 seconds: 81mph But loading the same file in SeeYou and looking at the data that pops up next to the mouse pointer and checking the speeds at the same points: +15 seconds: 13mph +20 seconds: 22mph +25 seconds: 33mph +30 seconds: 43mph Those are some rather drastic speed differences. The tow plane was one of Turf's Pawnees, which in the warmest weather don't have me sitting at 35 knots a full 30 seconds into the take-off roll. The distance algorithm I'm using is the classic Great Circle: distance_in_miles = 3956.0775034473 * arccos( SIN(lat1) * SIN(lat2) + COS(lat1)*COS(lat2) * COS(lng1-lng2) ) Any other hackers out there played with this stuff? -tw -- Using Opera's revolutionary e-mail client: http://www.opera.com/m2/ |
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