Paparazzi UAS  v5.15_devel-113-g1b57ff1
Paparazzi is a free software Unmanned Aircraft System.
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optical_flow_hover module

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.

Example for airframe file

Add to your firmware section:

1 <module name="optical_flow_hover"/>

Module functions

Init Functions

These initialization functions are called once on startup.

Files

Header Files

The following headers are automatically included in modules.h

Source Files

Raw optical_flow_hover.xml file:

<!DOCTYPE module SYSTEM "module.dtd">
<module name="optical_flow_hover" dir="ctrl">
<doc>
<description>
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.
</description>
</doc>
<settings>
<dl_settings>
<dl_settings name="OpticalFlowHover">
<dl_settings name="General">
<dl_setting var="cov_method" min="0" step="1" max="1" values="input|past" module="ctrl/optical_flow_hover" shortname="COV_METHOD" param="OFH_COV_METHOD"/>
<dl_setting var="hover_method" min="0" step="1" max="2" values="Sub|Same|Smart" module="ctrl/optical_flow_hover" shortname="HOVER_METHOD" param="OFH_HOVER_METHOD"/>
</dl_settings>
<dl_settings name="Vertical">
<dl_setting var="of_hover_ctrl_Z.cov_setpoint" min="-5.05" step="0.00001" max="0" module="ctrl/optical_flow_hover" shortname="covDiv_set_point" param="OFH_COVDIV_SETPOINT"/>
<dl_setting var="of_hover_ctrl_Z.ramp" min="0" step="0.005" max="1" module="ctrl/optical_flow_hover" shortname="rampZ" param="OFH_RAMPZ"/>
<dl_setting var="of_hover_ctrl_Z.reduction_factor" min="0.1" step="0.01" max="1" module="ctrl/optical_flow_hover" shortname="reduction_factorZ" param="OFH_REDUCTIONZ"/>
<dl_setting var="of_hover_ctrl_Z.PID.P" min="0" step="0.01" max="1" module="ctrl/optical_flow_hover" shortname="pgainZ"/>
<dl_setting var="of_hover_ctrl_Z.PID.I" min="0" step="0.001" max="0.1" module="ctrl/optical_flow_hover" shortname="igainZ" param="OFH_IGAINZ"/>
<dl_setting var="of_hover_ctrl_Z.PID.D" min="0" step="0.01" max="1" module="ctrl/optical_flow_hover" shortname="dgainZ" param="OFH_DGAINZ"/>
</dl_settings>
<dl_settings name="Horizontal">
<dl_setting var="of_hover_ctrl_X.cov_setpoint" min="-100000" step="100" max="10000" module="ctrl/optical_flow_hover" shortname="covFlow_set_pointX" param="OFH_COVDIV_SETPOINT"/>
<dl_setting var="of_hover_ctrl_Y.cov_setpoint" min="-100000" step="100" max="10000" module="ctrl/optical_flow_hover" shortname="covFlow_set_pointY" param="OFH_COVDIV_SETPOINT"/>
<dl_setting var="of_hover_ctrl_X.ramp" min="0" step="0.0001" max="0.05" module="ctrl/optical_flow_hover" shortname="rampX" param="OFH_RAMPXY"/>
<dl_setting var="of_hover_ctrl_Y.ramp" min="0" step="0.0001" max="0.05" module="ctrl/optical_flow_hover" shortname="rampY" param="OFH_RAMPXY"/>
<dl_setting var="of_hover_ctrl_X.reduction_factor" min="0.1" step="0.01" max="1" module="ctrl/optical_flow_hover" shortname="reduction_factorX" param="OFH_REDUCTIONXY"/>
<dl_setting var="of_hover_ctrl_Y.reduction_factor" min="0.1" step="0.01" max="1" module="ctrl/optical_flow_hover" shortname="reduction_factorY" param="OFH_REDUCTIONXY"/>
<dl_setting var="of_hover_ctrl_X.PID.P" min="0" step="0.00001" max="0.01" module="ctrl/optical_flow_hover" shortname="pgainX"/>
<dl_setting var="of_hover_ctrl_X.PID.I" min="0" step="0.00001" max="0.001" module="ctrl/optical_flow_hover" shortname="IgainX" param="OFH_IGAINX"/>
<dl_setting var="of_hover_ctrl_X.PID.D" min="0" step="0.00001" max="0.001" module="ctrl/optical_flow_hover" shortname="DgainX" param="OFH_DGAINX"/>
<dl_setting var="of_hover_ctrl_Y.PID.P" min="0" step="0.00001" max="0.01" module="ctrl/optical_flow_hover" shortname="pgainY"/>
<dl_setting var="of_hover_ctrl_Y.PID.I" min="0" step="0.00001" max="0.001" module="ctrl/optical_flow_hover" shortname="IgainY" param="OFH_IGAINY"/>
<dl_setting var="of_hover_ctrl_Y.PID.D" min="0" step="0.00001" max="0.001" module="ctrl/optical_flow_hover" shortname="DgainY" param="OFH_DGAINY"/>
<dl_setting var="oscphi" min="0" step="1" max="1" values="No|OSC" module="ctrl/optical_flow_hover" shortname="oscphi" />
<dl_setting var="osctheta" min="0" step="1" max="1" values="No|OSC" module="ctrl/optical_flow_hover" shortname="osctheta" />
<dl_setting var="derotated" min="0" step="1" max="1" values="Reg|Der" module="ctrl/optical_flow_hover" shortname="derotated" />
</dl_settings>
</dl_settings>
</dl_settings>
</settings>
<header>
<file name="optical_flow_hover.h" />
<file name="optical_flow_functions.h" />
</header>
<init fun="optical_flow_hover_init()" />
<makefile target="ap">
<file name="optical_flow_hover.c" />
<file name="optical_flow_functions.c" />
</makefile>
</module>