when landing on rising ground we don't want to use the terrain look
fwd correction for the flare calculation as otherwise we will flare
too early (and thus too high)
this allows for landings above or below the takeoff height without
requiring the use of terrain data. It allows both the use of vfwd
motor for holding against wind, and the correct height for land final
descent rate
Removes the need for plane to do the math for finding the relative height.
Also caches the value at the same time we update current_loc, which is a
non behaviour change as that was the only time you could see a change in
the relative height propegate through the system anyways
This doesn't count repeated readings towards the rangefinder count,
and resets the counter if the change is more than 20% of full
range. This greatly reduces the impact of poor sonar sensors for
landing
new param: LAND_ABORT_DEG
@Description: This parameter is used when using a rangefinder during landing for altitude correction from baro drift (RNGFND_LANDING=1) and the altitude correction indicates your altitude is higher than the intended slope path. Steeper slopes can result in crashes so this allows the option to remember the baro offset and self-abort the landing and come around for a another landing with the correct baro offset applied for a perfect slope. An auto-abort go-around will only happen once, next attempt will not auto-abort again. This operation happens entirely automatically in AUTO mode. This value is the delta degrees threshold to trigger the go-around. Example: if set to 5 deg and the mission planned slope is 15 deg then if the new slope is 21 then it will go-around. Set to 0 to disable. Requires LAND_SLOPE_RCALC > 0.
New param: LAND_SLOPE_RCALC
@Description: This parameter is used when using a rangefinder during landing for altitude correction from baro drift (RNGFND_LANDING=1) and the altitude correction indicates your altitude is lower than the intended slope path. This value is the threshold of the correction to re-calculate the landing approach slope. Set to zero to keep the original slope all the way down and any detected baro drift will be corrected by pitching/throttling up to snap back to resume the original slope path. Otherwise, when a rangefinder altitude correction exceeds this threshold it will trigger a slope re-calculate to give a shallower slope. This also smoothes out the approach when flying over objects such as trees. Recommend a value of 2m.
default value is 2 (so, enabled by default)