Getting more GPS fields: velocity, sensitivity and sample rate


for a project we are doing on measuring ocean waves it would be very useful to have the GPS velocity as well as sensitivity. This would together with an IMU + kalman filtering enable (hopefully) us to determine absolute direction of the acceleration (w/o magnetometer which is a bit more messy to use).

Is it possible to also get the velocity components from card.location. Ideally we’d like to know the quality of the GPS signal as well.

Is the GPS rate configurable? And would it be reliable to fetch it every 1Hz say? Or is it better to let the notecard log it to _track.qo?

Hi @gauteh,

If you look at the Asset Tracking guide, you’ll see velocity, bearing, and distance are added to tracking notes if card.location.mode is set to mode:continuous, OR if mode:periodic and seconds < 300.

As of firmware v3.2.1, GPS HDOP has been added to card.location responses.

You can also override a variety of GPS configurations via these environment variables.

Hope this helps!

Awesome! Great !

In continuous mode: what is the frequency of the GPS (couldn’t find that in the docs).?

GPS location data is only sampled if the Notecard detects movement based on the internal accelerometer. You can set the sensitivity of the accelerometer (which you probably already know) with the card.motion.mode API.

Ok. I was not aware. From the docs it seems like the position is sampled in periodic mode only if movement is detected, but in continuous mode this is not mentioned. But it makes sense that this has to be triggered by something as well… It is easier to work with regularly sampled data, what is the maximum frequency of the GPS if movement is detected in continuous mode? This device is going to move all the time, so it would be useful to know what frequency we should sample at.

The best scenario for us would be to just have the GPS output at its maximum frequency, regardless of movement.

Hi @gauteh - GPS location is sampled every 5 seconds (or less) when using continuous mode and motion is detected.