Using a Rangefinder for Autolanding¶
If you have fitted a rangefinder to your aircraft then you can use it for much more accurate landing control. To allow the rangefinder to be used for landing you need to set the RNGFND_LANDING parameter to 1. The first rangefinder with “down” orientation found, will be used.
When using a rangefinder for landing the altitude given by the rangefinder is used only in the landing approach and to determine the flare point, and is designed to allow the aircraft to more accurately follow the glide slope and to flare at the right time.
The effectiveness of a rangefinder can depend on the surface you are flying over, so it is a good idea to do some low passes in a flight mode such as FBWA first, then examine the logs to check that the rangefinder is working correctly.
Also note that if you have a longer range rangefinder then it is a very good idea to set the minimum range of the rangerfinder well above zero. For example, the PulsedLight Lidar has a typical range of over 40 meters, and when it gets false readings it tends to read ranges of less than 1 meter. And setting RNGFND1_MIN_CM to 150 , if its the first system rangefinder, will discard any rangefinder readings below 1.5 meters, and will greatly improve the robustness of the Lidar for landing.
If the autopilot has a good rangefinder (such as LIDAR) then you can safely choose quite small numbers for LAND_FLARE_SEC and LAND_FLARE_ALT, and flare closer to the ground than with the default values. That will generally produce a better landing.
A value for LAND_FLARE_SEC of 1.5 and LAND_FLARE_ALT of 2 is a good place to start with a LiDAR.