-- Copter attempts to fly home using dead reckoning if the GPS quality deteriorates or an EKF failsafe triggers
--
-- CAUTION: This script only works for Copter 4.3 (and higher)
-- this script checks for low GPS quality and/or an EKF failsafe and if either occurs, flies in the last known direction towards home
--
-- DR_ENABLE : 1 = enabled, 0 = disabled
-- DR_ENABLE_DIST : distance from home (in meters) beyond which the dead reckoning will be enabled
-- DR_GPS_SACC_MAX : GPS speed accuracy maximum, above which deadreckoning home will begin (default is 0.8). Lower values trigger with good GPS quality, higher values will allow poorer GPS before triggering. Set to 0 to disable use of GPS speed accuracy.
-- DR_GPS_SAT_MIN : GPS satellite count threshold below which deadreckoning home will begin (default is 6). Higher values trigger with good GPS quality, Lower values trigger with worse GPS quality. Set to 0 to disable use of GPS satellite count.
-- DR_GPS_TRIGG_SEC : GPS checks must fail for this many seconds before dead reckoning will be triggered.
-- DR_FLY_ANGLE : lean angle (in degrees) during deadreckoning. Most vehicles reach maximum speed at 22deg
-- DR_FLY_ALT_MIN : min alt (above home in meters) during deadreckoning. zero to return at current alt
-- DR_FLY_TIMEOUT : timeout (in seconds). Vehicle will attempt to switch to NEXT_MODE after this many seconds of deadreckoning. If it cannot switch modes it will continue in Guided_NoGPS. Set to 0 to disable timeout
-- DR_NEXT_MODE : flight mode vehicle will change to when GPS / EKF recovers or DR_FLY_TIMEOUT expires. Default is 6=RTL, see FLTMODE1 parameter description for list of flight mode number. Set to -1 to return to mode used before deadreckoning was triggered
-- How to use:
-- 1. set SCR_ENABLE = 1 to enable scripting (and reboot the autopilot)
-- 2. set SCR_HEAP_SIZE to 80000 or higher to allocate enough memory for this script
-- 3. set DR_ENABLE = 1 to enable dead reckoning
-- 4. optionally set DR_GPS_SACC_MAX and/or DR_GPS_SAT_MIN parameters to adjust how bad the GPS quality must be before triggering
-- 5. confirm "DR: waiting for dist (Xm < 50m)" message is displayed on ground station (so you know script is working)
-- 6. arm and takeoff to a safe altitude
-- 7. fly at least DR_ENABLE_DIST meters from home and confirm "DR: activated!" is displayed on ground station
--
-- If this script senses low GPS quality or an EKF failsafe triggers:
-- - vehicle will change to Guided_NoGPS mode
-- - vehicle will lean in the last known direction of home (see DR_FLY_ANGLE)
-- - if GPS recovers or EKF failsafe is cleared the vehicle will switch to DR_NEXT_MODE (if -1 then it will switch back to the mode in use before the GPS/EKF failure)
-- - if the timeout is surpassed (see DR_FLY_TIMEOUT) the vehicle will try to switch to DR_NEXT_MODE. If it fails to change it will continue in Guided_NoGPS but keep trying to change mode
-- - the pilot can retake control by switching to an "unprotected" mode like AltHold, Loiter (see "protected_mode_array" below)
--
-- Testing in SITL:
-- a. set map setshowsimpos 1 (to allow seeing where vehicle really is in simulator even with GPS disabled)
-- b. set SIM_GPS_DISABLE = 1 to disable GPS (confirm dead reckoning begins)
-- c. set SIM_GPS_DISABLE = 0 to re-enable GPS
-- d. set SIM_GPS_NUMSAT = 3 to lower simulated satellite count to confirm script triggers
-- e. set DR_GPS_SACC_MAX = 0.01 to lower the threshold and trigger below the simulator value which is 0.04 (remember to set this back after testing!)
--
-- Test on a real vehicle:
-- A. set DR_FLY_TIMEOUT to a low value (e.g. 5 seconds)
-- B. fly the vehicle at least DR_DIST_MIN meters from home and confirm the "DR: activated!" message is displayed
assert(param:add_param(PARAM_TABLE_KEY,2,'ENABLE_DIST',50),'could not add DR_ENABLE_DIST param')-- distance from home (in meters) beyond which the dead reckoning will be enabled
assert(param:add_param(PARAM_TABLE_KEY,3,'GPS_SACC_MAX',0.8),'could not add DR_GPS_SACC_MAX param')-- GPS speed accuracy max threshold
assert(param:add_param(PARAM_TABLE_KEY,4,'GPS_SAT_MIN',6),'could not add DR_GPS_SAT_MIN param')-- GPS satellite count min threshold
assert(param:add_param(PARAM_TABLE_KEY,5,'GPS_TRIGG_SEC',3),'could not add DR_GPS_TRIGG_SEC parameter')-- GPS checks must fail for this many seconds before dead reckoning will be triggered
assert(param:add_param(PARAM_TABLE_KEY,6,'FLY_ANGLE',10),'could not add DR_FLY_ANGLE param')-- lean angle (in degrees) during deadreckoning
assert(param:add_param(PARAM_TABLE_KEY,7,'FLY_ALT_MIN',0),'could not add DR_FLY_ALT_MIN param')-- min alt above home (in meters) during deadreckoning. zero to return at current alt
assert(param:add_param(PARAM_TABLE_KEY,8,'FLY_TIMEOUT',30),'could not add DR_FLY_TIMEOUT param')-- deadreckoning timeout (in seconds)
assert(param:add_param(PARAM_TABLE_KEY,9,'NEXT_MODE',6),'could not add DR_NEXT_MODE param')-- mode to switch to after GPS recovers or timeout elapses
