min_alt and max_alt?

[jmbalasalle]

Hi, this is fantastic work, great job.

I have a detailed question. It appears that you are using ground truth data to do the actual training. Specifically the values of min_alt and max_alt. These are read from the json file here. And these .json file are created by the create_satellite_dataset.py code here.

It therefore appears that when you are creating all the rays, you are using the min_alt and max_alt values (for the near and far planes). If we were to run this on a new or different AOI, that data would not be available. My question is this: how sensitive to these values is the code overall? Could we approximate these values using something like GTOPO30?

In the case of approximating min_alt and max_alt would we need to increase the number of sampling points on the rays?

I'm trying to run this on different areas, so I will probably try the approximation technique and see how it goes.

Thanks again for such a promising project!

[rogermm14]

Hello,

Thank you for your kind message and for bringing up this point. My intuition is the same as yours.

For new AOIs with no GT data I would go with some public elevation model to get reasonable values for min_alt, max_alt. E.g. task SRTM (check srtm4 !) at the central [lat, lon] point and subtract/add a reasonable margin that gives you an altitude range more or less suited to your target area.

Concerning the second question. Depending on how big the range is after defining min_alt and max_alt, yes, it may be wise to increase the number of sampling points (--n_samples). More samples will take more time though. In case it's of any use, in our AOIs we never exceeded 100m between min_alt and max_alt.

Good luck with your experiments !