removal of PX4_GZ_MODEL env variable and fix of ground glitching

[frede791]

Solved Problem

This PR solves two problems:

1. Reduces the number of environmental variables. Currently there exists PX4_GZ_MODEL and its alias PX4_SIM_MODEL. By replacing all instances PX4_GZ_MODEL with PX4_SIM_MODEL#*gz_ we can eliminate the need for PX4_GZ_MODEL.
2. When using the env variable PX4_GZ_MODEL_POSE (which previously could not be used with PX4_SIM_MODEL) the undefined pose position elements were filled up with 0. This leads to cases where models would clip into the ground, as described in [Bug] Vehicles glitching into the ground in Gazebo  #22214. This PR addresses this by checking whether the z-coordinate is less or equal to 0 and if that is the case, it will release the model at 1m above.

Question for @dagar and/or @beniaminopozzan: There are currently two instancees of PX4_GZ_MODEL being used in a debug file in platforms/posix/Debug/launch_sitl.json.in. Can you explain how removing the environmental variable PX4_GZ_MODEL would affect this?

Fixes #22214 (properly this time).

Solution

Replace PX4_GZ_MODEL with PX4_SIM_MODEL#*gz_

Changelog Entry

For release notes:

Removed/deprecated parameter: `PX4_GZ_MODEL`

Alternatives

We could also do a fancier pose calculation by reading it out of the sdf file that is provided. This may be more costly in terms of start up time.

[dagar]

Question for @dagar and/or @beniaminopozzan: There are currently two instancees of PX4_GZ_MODEL being used in a debug file in platforms/posix/Debug/launch_sitl.json.in. Can you explain how removing the environmental variable PX4_GZ_MODEL would affect this?

Honestly I'm not even sure anymore, I was hoping we could fully clean this up after the split between PX4 and model/gzserver as discussed.

[beniaminopozzan]

Thanks @frede791

Regarding your question, the instance of PX4_GZ_MODEL in platforms/posix/Debug/launch_sitl.json.in will not be affected by your changes. It is there just to let the user choose the GZ model they want to debug with.

[frede791]

@beniaminopozzan Thanks for the catch.

[beniaminopozzan]

Thanks @frede791 , LGTM.

Now, could you update the documentation too please?
https://docs.px4.io/main/en/sim_gazebo_gz/#syntax needs to be adjusted

[frede791]

@beniaminopozzan The user guide update is ready to go and @hamishwillee is just waiting for this to be merged.

[beniaminopozzan]

Thanks @frede791 !