Optical Flow uses a downward facing camera and a downward facing distance sensor for velocity estimation. Optical Flow based navigation is enabled by the estimators: EKF2 and LPE (deprecated).
An Optical Flow setup requires a downward facing camera and a distance sensor (preferably a LiDAR). These can be connected via MAVLink, I2C or any other bus that supports the peripheral.
The output of the flow when moving in different directions must be as follows:
|Vehicle movement||Integrated flow|
For pure rotations the
integrated_y) have to be the same.
PX4Flow is an optical flow camera that works indoors and and in low outdoor light conditions without the need for an illumination LED. It is one of the easiest and most established ways to calculate the optical flow.
PMW3901 is an optical flow tracking sensor similar to what you would find in a computer mouse, but adapted to work between 80 mm and infinity. It is used in a number of products, including some from: Bitcraze, Tindie, Hex, Thone and Alientek.
You can use any supported distance sensor. However we recommend using LIDAR rather than sonar sensors, because of their robustness and accuracy.
For optical flow fusion using EKF2, set the use optical flow flag in the EKF2_AID_MASK parameter, as shown using QGroundControl below:
If your optical flow sensor is offset from the vehicle centre, you can set this using the following parameters.
|EKF2_OF_POS_X||X position of optical flow focal point in body frame (default is 0.0m).|
|EKF2_OF_POS_Y||Y position of optical flow focal point in body frame (default is 0.0m).|
|EKF2_OF_POS_Z||Z position of optical flow focal point in body frame (default is 0.0m).|