This module implements monocular vision height estimation and uses this estimate to stabilize a quadrotor using only a downwards facing camera and an IMU. For scientific background please visit: https://repository.tudelft.nl/islandora/object/uuid%3A6e3ce742-a974-491d-97c2-1cafc090b3d9 The gain height relationship as first described in http://iopscience.iop.org/article/10.1088/1748-3190/11/1/016004 is calibrated in a controlled environment so that the resulting relationship can be used to determine the height at which the quadrotor is flying. In addition to the vertical axis the same principle is applied to the horizontal axes. A short guide on how to determine the slope: Picking a relatively high OFH_RAMP* with a very high negative OFH_COV*_SETPOINT (i.e. -6000000), looking at when the quadrotor starts oscillating, the respective message (covariances.*) should be used to determine a suitable threshold value for OFH_COV*_SETPOINT. The slope can then be decreased to gain accuracy in reaching the oscillations. Finally when flying the quadrotor on different heights the gain at which instability occurs can be noted to determine the slope of the gain-height relationship. Important settings: -OFH_HOVER_METHOD/hover_method: 0, the method is applied to all 3 axes in the following order: Z - X - Y 1, the method is applied to all 3 axes at the same time 2, the method is applied to the Z axis and the estimated height is used to determine the proper gains for the horizontal axes using the predetermined relationship. -XY_SYMMETRICAL is set to 1 if the drone is roughly symmetrical, causing the found gains for the X axis is also used for the Y axis. -OFH_*GAIN* can be used to set starting gains to prevent initial drift while still estimating height and appropriate gains. -OFH_REDUCTION* is used to reduce the gain after determining the oscillation to stabilize the quadrotor.