Attitude estimation doesn't start without baro sensor

[lukegluke]

For now baro data is essential to initialize height in Ekf::initialiseFilter() before switching to another source (GPS, etc.)
https://github.com/PX4/ecl/blob/5356077a3244a9a29adfae4aeaaab900cd28e9e8/EKF/ekf.cpp#L193

But it looks not really adoptable because filters will never get initialized for rovers that could have no baro sensor at all so the attitude estimator will not work (I don't dig enough yet - does attitude estimator itself needs height data?).

[bresch]

A source of vertical position and/or velocity is required to estimate the Z accel bias but not having a baro shouldn't block the whole EKF. Same for the mag: #800

[garlinplus]

Actualy if you hasn't a baro sensor,you can make a fake baro always witch 0 height,And you can get a attitude.

[lukegluke]

Yes, this is a workaround, but not the solution.

By the way for SYS_HAS_BARO and SYS_HAS_MAG parameters description says:
Disable this if the board has no magnetometer[barometer], such as the Omnibus F4 SD.
I wonder how ekf2 works on Omnibus F4 SD then?

[bresch]

I wonder how ekf2 works on Omnibus F4 SD then?

It doesn't, those drones are usually racers and use the "Q estimator" instead.

[bresch]

This will be fixed by #931 <= edit: the baro part didn't get merged in that PR

[priseborough]

We should fake a constant baro measurement with a larger uncertainty and set validity of vz and z to false so control loops don't try to use the height estimate.

[lukegluke]

@priseborough, I don't know if it is a suitable solution in general case (I'm working with rovers), but I workaround this issue by using gps height instead of baro (so no initialization until gps is valid) in Ekf::initialiseFilter() here.

PX4-ECL/EKF/ekf.cpp

Line 172 in b3fed06

// accumulate enough height measurements to be confident in the quality of the data

if (_params.vdist_sensor_type == VDIST_SENSOR_BARO) {
    // accumulate enough height measurements to be confident in the quality of the data
    if (_baro_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_baro_sample_delayed)) {
        if (_baro_sample_delayed.time_us != 0) {
            if (_hgt_counter == 0) {
                _baro_hgt_offset = _baro_sample_delayed.hgt;

            } else {
                _baro_hgt_offset = 0.9f * _baro_hgt_offset + 0.1f * _baro_sample_delayed.hgt;
            }

            _hgt_counter++;
        }
    }

} else if (_params.vdist_sensor_type == VDIST_SENSOR_GPS) {
    if (_gps_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_gps_sample_delayed)) {
        if (_gps_sample_delayed.time_us != 0) {
            if (_hgt_counter == 0) {
                _baro_hgt_offset = _gps_sample_delayed.hgt;

            } else {
                _baro_hgt_offset = 0.9f * _baro_hgt_offset + 0.1f * _gps_sample_delayed.hgt;
            }

            _hgt_counter++;
        }
    }
}

Of course it would better to check SYS_HAS_BARO instead.