Terrain following in DIY Posted June 10, 2019 · Edited June 10, 2019 by Spitfire76 · Report reply 4 hours ago, erfan said: This enables terrain following for RTL and LAND flight modes. It looks like both TERRAIN_ENABLE and TERRAIN_FOLLOW must be set to 1 for it to be enabled in RTL and LAND modes. By default it looks like they are set to 1 and 0 respectively. 4 hours ago, erfan said: Does that mean Even if I am using Teraranger evo 3 when landing it goes to 10 meter if setting waypoints using terrain ? Where do you get the 10 meter value from ?. Is that from the parameter LAND_ALT_LOW which defaults to 10m ?. This is of course used in autonomous landing and when reached will slow the decent to the value of LAND_SPEED. These are used to help provide a gentle landing. Its my understanding that without Terrain following enabled that 10 m would be 10 m above the home position. So say that the home position is 100 m above sea level (MSL) but you performed an autonomous landing on higher ground, at say 120m MSL, then the trigger to the slower decent speed would never be reached and maybe the UAV would bounce or even crash. With terrain following enabled this would be avoided as it would use the stored map data to know the height of the ground at that location although I understand that the data is not always that accurate which is why its better to have a rangefinder as that will know the true height above the ground or obstacle. Now one thing that comes to mind is that since the rangefinder is not used above RNGFND_MAX_CM which in your case is only 300 what happens above this height without terrain following enabled. Would it slow the decent at 3m instead of 10 m ?. I will have to check with SITL.