How are speed, altitude and heading actually calculated?

So I get there are logged points internally at a certain interval (like 1 min) and sent points which are sent out via satellite (like every 10 min).

So to get GPS speed you need at least to points:

A) So are those 2 points calculated from 2 successive logged points which in this case are 1 min apart?

B) Or is it calculated more instantaneously from say 2 or more GPS readings done maybe 1 sec apart like a normal GPS?

Altitude is via GPS or Baro or both?

Heading is calculated from a magnetic compass or from tracking points?

Thanks

0 frouwst over 4 years ago

OK after a bit of searching looks like the answer is A)

(i copy paste from the user "Twolpert")

Like all GPS devices, the Mini calculates distance along the track by adding up the straight-line distances between track points. The Mini records track points strictly according to time. If you have set the unit to "send" track points at 10 minute intervals and to "log" track points at one minute intervals, the Mini's idea of distance traveled will be based on the one-minute interval (the shorter of the send and log intervals).

The amount of inaccuracy that this introduces will depend on the shape of the track, the time between points, and your speed. There will be very little inaccuracy if the track is completely straight. That's never the case in practice. The straight-line distance between two points on a curved track is always less that the actual distance along the curve. More curves, higher speed and longer time between track points will all cause larger discrepancies.

On the Mini, it is possible to log at shorter intervals. But logging at 30 seconds or under will cause the Mini to keep the GPS radio on at all times. This drains the battery quickly. The Mini will display a warning if you set logging to 30 seconds or less.

And from the specs of the devices looks like electronic compass and barometer which is GPS calibrated.

0 carleson over 4 years ago in reply to frouwst

Explorer has a barometer. Mini does not so alt is GPS derived..