Prevents possible loss of attitude reference for flights without optical flow and GPS.
The optical flow measurement timeout can reset the velocity states which decouples the position states from IMU errors and therefore significantly reduces the amount of attitude error correction.
This enables the filter to report the last known position after disarm.
The LLH location of the filters NED origin is published and should be logged every time the vehicle is armed to assist with post-flight trajectory reconstruction.
The LLH location of the filters NED origin can be set externally whilst the vehicle is disarmed.
The two state auxiliary EKF has been replaced with a single state filter that only estimates terrain offset. The new filter fuses a optical flow line of sight rate scalar (length of the optical flow LOS rate vector) which provides a terrain offset estimate that is less affected by yaw errors.
Estimation of focal length scale factor error in flight wasn't accurate enough and will be replaced with a pre-flight intrinsic sensor calibration procedure as the scale factor error does not change over time provided the lens assembly is not adjusted.
AP_NavEKF: Remove unwanted printf
The terrain offset solution status is usable for a short period of time without state updates so a timeout has been added which prevents the rapid changes in solution status due to short duration sensor read errors.
This fixes a bug which could have caused the realative position status to be incorrectly reported under some conditions and also caused a compiler warning message. the logic used to report the filter solution status has been broken down into smaller, easier to understand statements.
Non user adjustable parameters are now declared as 'const' in the header.
The _ prefix has been removed from non user adjustable tuning parameters.
We use a function call rather than a constructor to initialise variables because it enables the filter to be re-started in flight if necessary.
For consistency some signed integer type declarations have been changed to unsigned where appropriate.
The decision to switch to constant velocity mode during optical flow operation and te decision to switch back were previously being made in two different places in code. Both decisions are now made in the one place which makes the code easier to follow and maintain.
Move velocity store out of optical flow to velocity and position fusion control as it is a velocity fusion function.
Always clear the previous mode status
This patch makes the reporting of an absolute position solution less abbiguaous and ensures that relative position is always true if absolute position is true
Because synthetic position measurements at 0,0 are fused during position hold mode, a position timeout cannot be used as the only means of detecting position solution status.
Andrew Tridgell
priseborough
Randy Mackay