SYS_STATUS GPS enabled flag not set by default

[julianoes]

PX4 does - by default - not set the flag SYS_STATUS.onboard_control_sensors_enabled for GPS.
https://mavlink.io/en/messages/common.html#SYS_STATUS

It only sets the flag if the param COM_ARM_WO_GPS is set to 0 meaning "Require GPS to arm".

I can see that by setting this param to 0 we make sure to only fly with GPS, however, I would argue, that whenever you switch to a mode which requires GPS, and relies on it, you essentially have the GPS "enabled". Or you could go as far as that if you run the GPS drivers, then clearly the GPS is "enabled.

For context: I've stumbled on this when implementing this flag in MAVSDK: mavlink/MAVSDK#1794
I can work around the oddity for now but - in my opinion - it is not really according to how I'd interpret the spec.

Here is where the flag is set:

PX4-Autopilot/src/modules/commander/Arming/PreFlightCheck/checks/ekf2Check.cpp

Line 241 in 5e1f62e

set_health_flags(subsystem_info_s::SUBSYSTEM_TYPE_GPS, gps_present, !arm_without_gps, gps_success, vehicle_status);

[dagar]

I don't really know how to interpret it either, but one idea I had was to capture configuration parameters per GNSS instance.
#19402

[junwoo091400]

I think checking the fix_type of the sensor_gps message would be reasonable. What do you think?

[junwoo091400]

Oops that would be about the health. Sorry!

[junwoo091400]

Or with SYS_HAS_GPS parameter? As that's how it's used in the ekf2Check:

https://github.com/PX4/PX4-Autopilot/blob/main/src/modules/commander/Arming/PreFlightCheck/checks/ekf2Check.cpp#L165-L166