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ardupilot/libraries/AP_Scripting/applets/ahrs-source-extnav-optflow.md

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ExternalNav / Optical flow source switching

Switches between AHRS/EKF sources based on the pilot's source selection switch or using an automatic source selection algorithm This script is intended to help vehicles automatically switch between ExternalNav and optical flow

Parmeter Descriptions

-- ESRC_EXTN_THRESH : ExternalNav innovation threshold -- ESRC_EXTN_QUAL : ExternalNav quality threshold -- ESRC_FLOW_THRESH : OpticalFlow innovation threshold -- ESRC_FLOW_QUAL : OpticalFlow quality threshold -- ESRC_RNGFND_MAX : Rangefinder altitude threshold (in meters)

How to use

Configure a downward facing lidar with a range of at least 5m Set RCx_OPTION = 90 (EKF Source Set) to select the source (low=ExternalNav, middle=opticalflow, high=Not Used) Set RCx_OPTION = 300 (Scripting1). When this switch is pulled high, the source will be automatically selected Set SRC_ENABLE = 1 (enable scripting) Set EK3_SRCn_ parameters so that ExternalNav is the primary source, opticalflow is secondary

  • EK3_SRC1_POSXY = 6 (ExternalNav)
  • EK3_SRC1_VELXY = 6 (ExternalNav)
  • EK3_SRC1_VELZ = 6 (ExternalNav)
  • EK3_SRC1_POSZ = 6 (ExternalNav) or 1 (Baro)
  • EK3_SRC1_YAW = 6 (ExternalNav) or 1 (Compass)
  • EK3_SRC2_POSXY = 0 (None)
  • EK3_SRC2_VELXY = 5 (OpticalFlow)
  • EK3_SRC2_VELZ = 0 (None)
  • EK3_SRC2_POSZ = 1 (Baro)
  • EK3_SRC2_YAW = 1 (Compass)
  • EK3_SRC_OPTIONS = 0 (Do not fuse all velocities)

When the 2nd auxiliary switch (300/Scripting1) is pulled high automatic source selection is used based on the following criteria:

  • ESRC_EXTN_THRESH holds the threshold for ExternalNav innovation threshold (around 0.3 is a good choice)

  • ESRC_EXTN_QUAL holds the ExternalNav quality threshold (about 10 is a good choice)

  • ESRC_FLOW_QUAL holds the optical flow quality threshold (about 50 is a good choice)

  • ESRC_FLOW_THRESH holds the threshold for optical flow innovations (about 0.15 is a good choice)

  • ESRC_RNGFND_MAX holds the threshold (in meters) for rangefinder altitude

  • If ExternalNav's quality is above ESRC_EXTN_QUAL and innovations are below ESRC_EXTN_THRESH, ExternalNav is used

  • Optical flow is used if the above is not true and:

    • Quality is above ESRC_FLOW_QUAL
    • Innovations are below ESRC_FLOW_THRESH
    • Rangefinder distance is below ESRC_RNGFND_MAX