Update ROI of warp map using initUndistortRectifyMap()

[Steve_in_Denver]

@crackwitz

I see no reason why initUndistortRectifyMap would reallocate the map matrices you pass in, if they’re the correct size and type already. you just have to make sure the other parameters don’t change in any way that would make that necessary.

it should be able to update those maps in-place.

Yes, you are correct. It took me a while to track down my error, but once I did it started working as expected.

My error: I had created both maps as CV_16SC2 type, but the second map needs to be CV_16UC1.

So this is great news for me - I think I can do exactly what I want. Sorry for the confusion, and thanks for the help.

-Steve