This adds a large amount of noise robustness to the compass offset
learning algorithm, at a cost of 120 bytes of memory. The changes are
based on a long discussion with Bill Premerlani.
this seems to work much better than the old algorithm, converging
faster and more accurately. Even better, it has no linkage to DCM, so
no possibility of nasty feedback effects
This will set the declination based on lat/lon if the user has
not yet saved one to the EEPROM, OR if they have specified via the
config parameter that they want it to overwrite the declination every
3D fix.
Signed-off-by: Andrew Tridgell <tridge@samba.org>
these allow you to control if the compass should be used for yaw and
if it should learn its offsets. This is useful for locking in compass
offsets once they are confirmed to be good, and for learning offsets
without using them in flights.
The default is to behave the same as previously, which is
COMPASS_LEARN=1 and COMPASS_USE=1
Since the magnetometer offsets are not available through the MAVLink parameter interface (since they are an AP_Var vector) this little feature allows them to be reset from the CLI. Useful if you somehow get bad offsets or if you change magnetometer. If you have a bad set of large offset values I have seen issues with the nulling algorithm have trouble converging to the proper values. I have never seen it have trouble converging from 0/0/0, so this could be a useful feature from time to time.
This is a fix for an interesting bug when a DCM matrix reset was added to the ground start. This bug only showed up if (A) a ground start were performed after an air start or due to use of the "Calibrate Gryo" action, (B) if the current orientation were sufficiently different from 0/0/0, and (C.) if the particular magnetometer had sufficiently large offsets. Why did resetting the DCM matrix to 0/0/0 pitch/roll/yaw at ground start cause a bug? The magnetometer offset nulling determines the proper offsets for the magnetometer by comparing the observed change in the magnetic field vector with the expected change due to rotation as calculated from the rotation in the DCM matrix. This comparison is made at 10Hz, and then filtered with a weight based on the amount of rotation to estimate the offsets. Normally it would take considerable time at normal in-flight rotation rates for the offset estimate to converge.
If a DCM matrix reset occurs when the offset nulling algorithm is up and running, the algorithm sees the DCM reset as a instantaneous rotation, however the magnetic field vector did not change at all. Under certain conditions the algorithm would interpret this as indicating that the offset(s) should be very large. Since the "rotation" could also have been large the filter weighting would be large and it was possible for a large erroneous estimate of the offset(s) to be made based on this single (bad) data point.
To fix this bug methods were added to the compass object to start and stop the offset nulling algorithm. Further, when the algorithm is started, it is set up to get fresh samples. The DCM matrix reset method now calls these new methods to stop the offset nulling before resetting the matrix, and resume after the matrix has been reset.
Most of the compass functionality is now abstracted in a base class, with the various sub-classes implementing just their unique functionality.
git-svn-id: https://arducopter.googlecode.com/svn/trunk@1647 f9c3cf11-9bcb-44bc-f272-b75c42450872
Andrew Tridgell
Adam M Rivera
Doug Weibel
rmackay9@yahoo.com
deweibel@gmail.com
james.goppert
jasonshort
DrZiplok@gmail.com
DrZiplok
deweibel