[jrockway]

You don't need to do any geometry. Your GPS module will simply output the speed.

While you can calculate based on position fixes, it is more accurate for the GPS to do it. It does not do a simple distance/time calculation but can instead look at the phase / doppler shift of the GPS signals. This ends up being much more accurate.

[slicktux]

Thanks for the reply; did not think about that and after all that is the crucial characteristic of what allows GPS to work: now does it depend on the GPS module? Or can phase and Doppler shift be accesses regardless of the device?

[dvdbloc]

Every consumer GPS receiver I have seen and even some aerospace-grade receivers that I have (limited) experience with report data over a serial connection as “NMEA sentences”. You can read about them here: https://www.gpsinformation.org/dale/nmea.htm#nmea if it’s a USB GPS receiver, it’s likely internally a USB->serial chip with a GPS receiver communicating over serial. The data that I have seen is always been high-level focused on navigation such as speed in MPH and heading in degrees and of course, long and lag. Not to say that you can’t find a device that reports phase and Doppler shift, this is just how everything I have seen worked. When GPS receivers started getting cheap when I was a kid, I was very excited to experiment with them using Arduinos, etc so hope this helps!

[slicktux]

Thank you for the information! I will be giving this a read! Can’t wait!

[JensRex]

If you want to do anything with GPS modules, some fine and talented people have done the hard work of interfacing with, and parsing the output of a lot of different receivers, and called it `gpsd`.

https://gpsd.gitlab.io/gpsd/index.html

[lultimouomo]

It definitely depends on the device. You can find a lot of information about Doppler GPS in speed record communities on the internet, e.g. in this speed surfing record tracker:

https://www.gps-speedsurfing.com/default.aspx?mnu=item&item=...

[slicktux]

Another excellent reply! Thank you! This will definitely come in handy for personal projects; like autonomous robots; it helps to have redundant systems and it seems that GPS is more accurate than odometry or accelerometers that suffer from drift