Paparazzi UAS  v5.15_devel-88-gb3ad7fe
Paparazzi is a free software Unmanned Aircraft System.
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optical_flow_landing module

Optical flow landing.

This module implements optical flow landings in which the divergence is kept constant (for rotorcraft). When using a fixed gain for control, the covariance between thrust and divergence is tracked, so that the drone knows when it has arrived close to the landing surface. Then, a final landing procedure is triggered. It can also be set to adaptive gain control, where the goal is to continuously gauge the distance to the landing surface. In this mode, the drone will oscillate all the way down to the surface.

de Croon, G.C.H.E. (2016). Monocular distance estimation with optical flow maneuvers and efference copies: a stability-based strategy. Bioinspiration and Biomimetics, 11(1), 016004.

Example for airframe file

Add to your firmware section: This example contains all possible configuration options, not all of them are mandatory!

1 <module name="optical_flow_landing">
2  <define name="OFL_AGL_ID" value="ABI_BROADCAST" />
3 </module>

Module configuration options

Define Options

  • name: OFL_AGL_ID value: ABI_BROADCAST
    Description: Sender id of the AGL (sonar) ABI message

Airframe file section

  • section name: OFL prefix: OFL_
    • name PGAIN value: 0.50
      Description: P gain on height error
    • name IGAIN value: 0.10
      Description: I gain on summed height error
    • name DGAIN value: 0.0
      Description: D gain on summed height error
    • name VISION_METHOD value: 1
      Description: 0 = fake vision, 1 = real vision
    • name CONTROL_METHOD value: 2
      Description: 0 = fixed gain control, 1 = adaptive gain control, 2 = exponential control
    • name COV_METHOD value: 0
      Description: 0 = cov(uz, div), 1 = cov(div_past, div)
    • name COV_WINDOW_SIZE value: 30
      Description: Number of time steps for window size for getting the covariance over time.
    • name COV_LANDING_LIMIT value: 2.2
      Description: Covariance where the vehicle engages final landing procedure.
    • name COV_SETPOINT value: -0.0075
      Description: Target Covariance for adaptive gain increment.
    • name LP_CONST value: 0.75
      Description: Low pass filter constant for divergence input.
    • name ELC_OSCILLATE value: true
      Description: Oscillate to find optimum gain before initiating landing.

Files

Header Files

The following headers are automatically included in modules.h

Source Files

Raw optical_flow_landing.xml file:

<!DOCTYPE module SYSTEM "module.dtd">
<module name="optical_flow_landing" dir="ctrl">
<doc>
<description>
Optical flow landing.
This module implements optical flow landings in which the divergence is kept constant (for rotorcraft). When using a fixed gain for control, the covariance between thrust and divergence is tracked, so that the drone knows when it has arrived close to the landing surface. Then, a final landing procedure is triggered. It can also be set to adaptive gain control, where the goal is to continuously gauge the distance to the landing surface. In this mode, the drone will oscillate all the way down to the surface.
de Croon, G.C.H.E. (2016). Monocular distance estimation with optical flow maneuvers and efference copies: a stability-based strategy. Bioinspiration and Biomimetics, 11(1), 016004.
</description>
<define name="OFL_AGL_ID" value="ABI_BROADCAST" description="Sender id of the AGL (sonar) ABI message"/>
<section name="OFL" prefix="OFL_">
<define name="PGAIN" value="0.50" description="P gain on height error"/>
<define name="IGAIN" value="0.10" description="I gain on summed height error"/>
<define name="DGAIN" value="0.0" description="D gain on summed height error"/>
<define name="VISION_METHOD" value="1" description="0 = fake vision, 1 = real vision"/>
<define name="CONTROL_METHOD" value="2" description="0 = fixed gain control, 1 = adaptive gain control, 2 = exponential control"/>
<define name="COV_METHOD" value="0" description="0 = cov(uz, div), 1 = cov(div_past, div)"/>
<define name="COV_WINDOW_SIZE" value="30" description="Number of time steps for window size for getting the covariance over time."/>
<define name="COV_LANDING_LIMIT" value="2.2" description="Covariance where the vehicle engages final landing procedure."/>
<define name="COV_SETPOINT" value="-0.0075" description="Target Covariance for adaptive gain increment."/>
<define name="LP_CONST" value="0.75" description="Low pass filter constant for divergence input."/>
<define name="ELC_OSCILLATE" value="true" description="Oscillate to find optimum gain before initiating landing."/>
</section>
</doc>
<settings>
<dl_settings>
<dl_settings NAME="OpticalFlowLanding">
<dl_setting var="of_landing_ctrl.nominal_thrust" min="0" step="0.001" max="1" module="ctrl/optical_flow_landing" shortname="nominal_thrust"/>
<dl_setting var="of_landing_ctrl.lp_const" min="0.005" step="0.005" max="1" module="ctrl/optical_flow_landing" shortname="lp_factor" param="OFL_LP_CONST"/>
<dl_setting var="of_landing_ctrl.divergence_setpoint" min="-1" step="0.01" max="1" module="ctrl/optical_flow_landing" shortname="div sp"/>
<dl_setting var="of_landing_ctrl.cov_set_point" min="-6" step="0.0001" max="6" module="ctrl/optical_flow_landing" shortname="cov_set_point" param="OFL_COV_SETPOINT"/>
<dl_setting var="of_landing_ctrl.cov_limit" min="0" step="0.0001" max="6" module="ctrl/optical_flow_landing" shortname="cov_limit" param="OFL_COV_LANDING_LIMIT"/>
<dl_setting var="of_landing_ctrl.pgain" min="0" step="0.001" max="6" module="ctrl/optical_flow_landing" shortname="pgain" param="OFL_PGAIN"/>
<dl_setting var="of_landing_ctrl.igain" min="0" step="0.001" max="1" module="ctrl/optical_flow_landing" shortname="igain" param="OFL_IGAIN"/>
<dl_setting var="of_landing_ctrl.dgain" min="0" step="0.1" max="6" module="ctrl/optical_flow_landing" shortname="dgain" param="OFL_DGAIN"/>
<dl_setting var="of_landing_ctrl.VISION_METHOD" min="0" step="1" max="1" values="Ground truth|Online" module="ctrl/optical_flow_landing" shortname="VISION_METHOD" param="OFL_VISION_METHOD"/>
<dl_setting var="of_landing_ctrl.CONTROL_METHOD" min="0" step="1" max="2" values="Simple|Adaptive|Exp" module="ctrl/optical_flow_landing" shortname="CONTROL_METHOD" param="OFL_CONTROL_METHOD"/>
<dl_setting var="of_landing_ctrl.COV_METHOD" min="0" step="1" max="1" values="Div-Thrust|Div-Shift div" module="ctrl/optical_flow_landing" shortname="COV_METHOD" param="OFL_COV_METHOD"/>
<dl_setting var="of_landing_ctrl.delay_steps" min="0" step="1" max="60" module="ctrl/optical_flow_landing" shortname="delay_steps"/>
<dl_setting var="of_landing_ctrl.pgain_adaptive" min="0" step="0.1" max="20.0" module="ctrl/optical_flow_landing" shortname="pgain_adaptive"/>
<dl_setting var="of_landing_ctrl.igain_adaptive" min="0" step="0.01" max="1.0" module="ctrl/optical_flow_landing" shortname="igain_adaptive"/>
<dl_setting var="of_landing_ctrl.dgain_adaptive" min="0" step="0.01" max="5.0" module="ctrl/optical_flow_landing" shortname="dgain_adaptive"/>
<dl_setting var="of_landing_ctrl.reduction_factor_elc" min="0.1" step="0.01" max="3.0" module="ctrl/optical_flow_landing" shortname="reduction_factor_elc"/>
<dl_setting var="of_landing_ctrl.elc_oscillate" min="0" step="1" max="1" values="FALSE|TRUE" module="ctrl/optical_flow_landing" shortname="oscillate" param="OFL_ELC_OSCILLATE"/>
</dl_settings>
</dl_settings>
</settings>
<header>
<file name="optical_flow_landing.h"/>
</header>
<makefile target="ap">
<file name="optical_flow_landing.c"/>
</makefile>
</module>