SparkFun Forums

[ITM]

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

[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.

[ITM]

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