I am concerned about the elevation accuracy of the terrain follow feature. I plan to fly from the foothills into mountains with steep valleys with alot of elevation changes. In the United States in the srtm data base that is linked from ardupilot wiki is accuracy down to one arc second? Or is the whole data base 3 arc second tiles. I want to know if the tiles are 100m is the whole tile the flight controller sees one elevation. Is the elevation the average of the tile? If I’m flying down a narrow canyon and rtl kicks in will it see the canyon wall and know not to turn around until it clears or am I going to have to set the rtl_climb_min enough to clear the canyon walls before turning around? Is it best to have a certain amount of room around the plane for error in elevation data? I think I read in the wiki it says to be at least 50m above ground when using terrain follow would that also include to the left and right of the plane? Any info on the ardupilot srtm data base would be appreciated greatly.
Thank you for your time.
I have found in 2014 and 2015 the srtm project release a map with accuracy down to 1 arc second or 30m tile spacing. Can I use srtm data from another source ? Will it still work?
hai @AeRiAL_PeRpLeXiOn sir,
It is better to use range finder for terrain flow.
If already you did terrain flow with sensor(lidar or radar). skip this.
Thanks and regards
Mohan
Thanks for replying, I’m assuming from the silence, that your answer is about all the trust I should have in terrain follow while doing low altitude operations.
When a craft is fitted with a range finder does the craft use that range when in rtl or flight modes over terrain follow? Would one disable terrain follow while range find in on craft?
If by narrow canyon you mean with a width less than at least three times the resolution of the dataset, i wouldnt trust it. Furthermore, i would suggest to use a rally point down the canyon alignment so the carft goes to the rally point instead of home.
Yes the elevation is average of the tile.
If you have a higher resolution dataset, you can use that but make sure it is referenced to wgs84 datum.
No you would not disable terrain follow with a rangefinder. Rangefinders only job is to provide you with the range to the terrain. With the rangefinder, you will only make sure any incorrect elevations of the srtm dataset are ignored.
I personally have not used terrain following till now but I assume thats how it goes. I would suggest more careful reading of the feauture in the wiki though. Goodluck.
In 2014 and 2015 the srtm release 1 arc second maps for the whole earth between 60°north and 54°south. 1 arc second at the equator is 30m. The srtm maps are easy to find on google. I just need to research how wgs84 datum fits into the srtm maps
Generally speaking, other datasets may have another datum specified. You would just have to transform it.
I believe the terrain generator on ardupilot is based on the SRTM data which uses wgs84 coordinates.
The vertical datum used is EGM96. Any data you use should also use these vertical and horizontal datums.
EGM96 is basically a GEOID linked to the WGS84 datum.