Hello everyone,

I'm trying to use the TERRAIN FOLLOWING for the first time.

I'm following the documentation here > http://planner.ardupilot.com/wiki/common-terrain-following, but I find it quite incomplete.

First question, is there an alternative with a step-by-step description of how to get this function running correctly?

To my other questions:

- Is a GPS lock a precondition for the terrain to start uploading to the auto-pilot (pixhawk)?
The thing is, I have to prepare a mission at a place I do not get GPS fix. I do no see any terrain data being uploaded or updated after defining a mission and uploading it to the auto-pilot

- And with this, I come to my next question. Do I understand right, that in order to get the data uploaded to the APM, I need to have my ground station with the MP connected to the internet?
If I'm working in remote areas where there is no mobile internet connection and the mission areas are so big I cannot upload everything a priori to the auto-pilot, how can I assure that the SRTM data is stored on my GS-laptop?

So, these are my first questions...

Can some one help me on this,

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The TF feature is not available on the APM, it is only on the Pixhawk.

Sorry, my mistake, I have been using APM to designate the auto-pilot, not the product. Bad choice. I'll change my text to avoid confusion. I'm using Pixhawk

I believe that if you have prefetched your mission, you do NOT need to be connected to the internet.

To add to your questions, I would like to see, in MP, a spatial graph, while flying or terrain and aircraft, much the same as MP Elevation graph.

It would also be helpful to see a YouTube of planning a Terrain Following mission, including validating it will work. I have had the misfortune of a F/S with Terrain Follow active and the plane just plowed into the ground. This is why I would like to see a graph in MP using the programmed "look ahead". Then one could see if the TF was going to work BEFORE running into a mountain.

So, do I understand it right, that when caching google maps, for instance (or some other available layer), MP will also cache the SRTM elevation data, so that it will be available of the field offline?

I do not know if the developers of MP are reading this, or if I have to go to github to ask the following question, but:

is there some development priority in function of fundings? I.e. if I manage to organize funding to develop a certain functionality, would this be possible?

I must be honest, I do not know the background of the MP development team, which companies are involved, etc. But I know from other open-source projects, that if the community is able to fund a certain functionality in the software, this will also be implemented with higher priority for a certain amount of money. 

Just asking to understand how it works in this case....

Yes, that's how I think it works. I cache the area I plan to fly for the mission and at the field, on MP, I see the terrain data being uploaded to the ***hawk.

But I would like to see a video tutorial of doing a compete Terrain follow mission from MP param settings and MP readouts. Also, a F/S action with the plane flying over an obstacle due to the Terrain following feature. As I mentioned, this failed me and I crashed. Never really go an answer.


I have done some testing concerning the caching of elevation data in the MP.

So, what seems to be clear

  • independently of which map resource I use, MP loads the elevation data (which comes from google, correct?) - . I did not test all, surely, but around 3 different layers and each time the elevation data is downloaded. That's fine!
  • If I go off line the data continue being available. Also nice!

What does not seem to be clear are the following points (&Questions)

  • It is not clear to me, if MP loads elevation data above a certain zoom level. I have the feeling it does not load anything, since it indicates me altitude zero everywhere. So my question is: Is there a zoom-in-threshold that has to be overcome in order for MP to start loading the altitude data?
  • Related with the previous point is the following question: Does MP load elevation data always with the same resolution? I.e. if we are in a region where the SRTM grid is of 30 m, will MP load the data with this resolution independently of the zoom level? Because this would explain the previous observation. If the zoom level is very low, the amount of data being fetched is huge, so it will take decades to have it available for the portion of map being showed in MP. The reason why I'm saying this is that when I slowly zoom in, there are regions of the map which start showing elevation data, other not (i.e. values=0). It seems to take some time until the whole map is populated with values.
  • And this brings me to my last point. MP shows when all map tiles are loaded (check image), but this does not mean that the elevation grid was completely loaded. This can be very irritating, since you have to sweep the whole area with your mouse to be really sure that the elevation data was stored locally. I suggest introducing also an indication informing the user if elevation data are still being loaded or if the grid is complete. That would be very useful! (Where on GITHUB can I propose such a feature?)


There's not a lot of info around but one of the best is the original post by Tridge: http://diydrones.com/profiles/blogs/terrain-following-added-to-apm-... and the comments therein.

srtm data is downloaded in 1 degree by 1 degree squares.

1 degree lat = ~ 110km

srtm tiles are downloaded if the zoom level is above 12 in the flight planner view.


First question: is there somewhere an indication about the zoom level in MP?

Second question: Do you really mean it when you say the resolution of the srtm is around 100 x 100 Km². That cannot be... As far as I understand it, the publicly available srtm has a global resolution of 90 x 90 m² (and 30 x 30 m² in selected areas, e.g. US).  Ok, maybe I'm misunderstanding your text, you mean the the overall area for which srtm data with 90 m resolution is downloaded at one time is of 100 x 100 Km²..... so even if I'm looking at a region of 10 x 10 Km², MP will fetch the data for a 100 x 100 Km² square.

What happens if I'm looking at an area bigger than the 100 x 100 Km²?


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