# GPS Speed in ONE Axis

Hi,

I am working on a project in which want to measure the vertical height of a jump in kitesurfing.

(I am also considering other Sensors like Acc/Gyro/Baro)

A sensor I would like to use is a GPS-Sensor. Due to the fact the 3D position measurement by GPS has an average error of ~2 metres, it is not precise enough. Instead I´d like to use the GPS-Speed-Data. The Speed-Data measured by GPS is much more precise, as it is based on Doppler-Shifting-Technology.
(How Does GPS Work? - RACELOGIC Support Centre)

Looking at the Outputs from GPS-Sensors you find that they only give you one "Speed"-Value. That leads to my questions: Does this speed value contain all speeds in all 3 Axis? Does it only measure horizontal speed? Does it measure vertical speed (Z-Axis)?

Is there a way to get the speed-measurement in only axis (in my case of measuring a jump: Z-Axis) from a GPS-Sensor?

The Speed-Data measured by GPS is much more precise, as it is based on Doppler-Shifting-Technology.

The speed data returned by most cheap GPS units is derived from the position data.

Take a look at chapter 1.8 of this datasheet: https://www.u-blox.com/sites/default/files/NEO-M8_DataSheet_(UBX-13003366).pdf

It seems like Doppler-Velocity is considered in some way. This is a very common GPS-Module.

Best Regards

An average 3D error of 2M is surely fantasy, height error alone can easily be 10-30M or more between fixes.

2m is not fantasy.

Even better, if the GPS chip is doing the doppler thing then it uses that to calculate position too. So short term errors like "how much higher am I than 2 seconds ago" will be very much smaller. Maybe a centimeter if only measuring differences in altitude.

The speed is a horizontal measurement, not useful for vertical measurements.

Altitude is very poorly determined by GPS. The altitude error is often 10 or more times higher than the horizontal error.

Due to the fact the 3D position measurement by GPS has an average error of ~2 metres

Under the very best of circumstances, sometimes, and then only with DGPS stations in range.

Indeed, barometers are used for height stabilization in quadcopters because GPS will simply crash the thing!

Perhaps a barometer is what you need?