Fake GPS Velocity Frame Issue

[jgoppert]

We are using fake GPS on PX4 and noticed that we get drift and high velocity residuals. We are still testing further, but suspect these lines. The velocity is calculated using a single step finite difference approximation. vel = ([pos[t_1] - pos[t_0]) / dt. The problem is that the frame is incorrect. These positions are in earth centered, earth fixed coordinates. This is not the north east down coordinate system. As soon as we move from hover, our residuals spike. We will submit a patch after test flying it.

https://github.com/mavlink/mavros/blob/c035b8ff1ffb042db235648371f5d7d2e531fae4/mavros_extras/src/plugins/fake_gps.cpp#L309 https://github.com/mavlink/mavros/blob/c035b8ff1ffb042db235648371f5d7d2e531fae4/mavros_extras/src/plugins/fake_gps.cpp#L343

MAVROS version and platform

Mavros: Master ROS: Noetic Ubuntu: 20.04

[Alefunk]

This is related: #1639