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Tips and questions relating to the GPS modules from SFE
Hi !

The only way to get a speed from NMEA messages is using VTG message. The speed returned is "speed relative to the ground".
Since I'm using a lassen IQ, the only way to get the "air" speed is using TSIP messages right?
I could get North, East and Up velocity, and then calculate the "air" speed. Is this the good way to do that?
Thanks in advance
By mramsey
The VTG sentence gives you "ground speed" and "ground track". TSIP messages gives you north-south "ground speed", east-west "ground speed" and vertical velocity relative to the surface. If your are interested om calculating absolute speed in 3 dimensions, TSIP will do the job.

To get "air speed" in the aircraft sense you need a differential pressure sensor and pitot tube. A GPS can not directly measure airspeed, as air speed is a measurement of dynamic pressure, which varies according to the wind, ambient pressure, and temperature.
Oh of course you're right !
Actually I was interessed in 3d speed, but I forgot about pressure for air speed "measures".
Thanks, I've switched succesfully to TSIP protocol, I can calculate 3D speed now :)
Edit : BTW, that's a bad thing to loose the easy to read ZDA messages... It's seems so complicated with week numbers :(
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