Convert uncertainty in initial rotate vector into quaternion covariances using symbolic toolbox derived expressions.
Enable setting of initial angle uncertainty via a parameter
Convert quaternion covariances into an angular alignment variance vector and discard the z component so that yaw uncertainty does not affect the result.
Replace the delayed time feedback mechanism used by the translational states with a direct feedback method.
Time constants for velocity and position convergence can be separately adjusted with tunable parameters
The method is more computationally more expensive because it requires modification of the output buffer history but is acceptable because it only requires 6 FLOP per buffer index for a total of 30*6 = 180 FLOP
The method was not applied to the attitude states because the quaternion operations required at each buffer index would have been computationally prohibitive.
Combines the forced symmetry, variance limiting and zeroing of covariances for unwanted states in the one function.
This ensures a consistent correction is applied after every covariance prediction or correction.
With the EKF, the average update rate is more important than the instantaneous value as it affects tuning. This patch ensures that the EKF prediction cycle will be performed early if the previous one was late in an attempt to maintain the target update rate.
This method is more suitable than a raw heading measurement because it works across a full range of pitch angles.
It has been made the default for ground operation.
The position reset was not being compensated for velocity and measurement delay
The height was being reset with the position. It has been moved into a separate reset function
The maximum accepted GPS delay of 100msec was inadequate
The states was being incorrectly reset to the GPS position and Baro height on initial alignment.
When fusing 3-axis magnetometer data without absolute external aiding leg GPS), the declination is ultimately unobservable and the declination of the field states and the vehicle heading will slowly drift over time. To prevent this we need to fuse in a declination to constraint the NE earth field estimates.
Use of the power function to square a number can be very inefficient depending on processor and compiler. Replace with an inlined function that multiplies the number by itself. This has not been put into the maths library because the use of the sq() function is peculiar to the autocode generated for the EKF and an inlined function was desired.
Paul Riseborough
Roman Bapst
CarlOlsson
mcsauder
bugobliterator
Roman