About RPC generation using cam2rpc

[Jongmin Kim]

Dear ASP community,

I'm trying to create an RPC using the cam2rpc tool. (LROC NAC image)

However, I'm facing an issue as there is no separate DEM available.

So, while searching through old documentation, I found that I can use the level 2(map.cub) image generated by ISIS's cam2map instead of a DEM.

I succeeded in creating the RPC using this method, but I have doubts about how accurate the extracted RPC coefficients are, especially the height scale and height offset

Is there someone who has generated RPC with level 2(map.cub) image?

Also, I'm curious if anyone has attempted to use LDEM(LOLA DEM) for this purpose.

Best regards,
Kim

[Oleg Alexandrov]

You are using the map.cub image as a DEM, so the pixel values are heights, in meters. That is not bad as a first guess.

What you can do is mapproject your original cub file (not the mapped one) onto this "DEM", and do the same with the new RPC camera. For that it may be better to rename your level2.map.cub to something like dem.tif, and do:

 mapproject  dem.tif input.cub input_rpc.xml output_rpc.tif

and compare that with the earlier result, of mapproject of the input.cub without rpc. They should agree.

The section https://stereopipeline.readthedocs.io/en/latest/tools/cam2rpc.html#validation also has example of validation of your input.cub vs the RPC camera using rays traced from the camera and back.

Also note that cam2rpc can be used without a DEM. One can use a lon-lat range and height range. Then it will try to fit to every point in that ground box. The documentation has an example.

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