What does the "ahrs-source" script do from the documentation

Acsell · July 25, 2023, 2:52pm

Hello, I came across an example from the documentation, and I don’t fully understand how it works, and what exactly does it do?

github.com

ArduPilot/ardupilot/blob/master/libraries/AP_Scripting/examples/ahrs-source.lua

-- 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 move between GPS and Non-GPS environments
--
-- setup RCx_OPTION = 90 (EKF Pos Source) to select the source (low=primary, middle=secondary, high=tertiary)
-- setup RCx_OPTION = 300 (Scripting1).  When this switch is pulled high, the source will be automatically selected
-- setup EK3_SRCn_ parameters so that GPS is the primary source, Non-GPS (i.e. T265) is secondary and optical flow tertiary
-- configure a forward or downward facing lidar with a range of more than 5m
--
-- When the auxiliary switch (ZigZag Auto) is pulled high automatic source selection uses these thresholds:
-- SCR_USER1 holds the threshold for rangefinder altitude:
--     if rangefinder distance >= SCR_USER1, source2 (ExtNav) will be used (if Non-GPS vel innovations are good)
--     if rangefinder distance < SCR_USER1, source3 (optical flow) will be used (if Non-GPS vel innovations are not good)
-- SCR_USER2 holds the threshold for GPS speed accuracy (around 0.3 is a good choice)
-- SCR_USER3 holds the threshold for Non-GPS vertical speed innovation (about 0.3 is a good choice)
--     if both GPS speed accuracy <= SCR_USER2 and ExternalNav speed variance >= SCR_USER3, source1 will be used
--     otherwise source2 (T265) or source3 (optical flow) will be used based on rangefinder distance
-- luacheck: only 0

local rangefinder_rotation = 25     -- check downward (25) facing lidar
local source_prev = 0               -- previous source, defaults to primary source

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