extrapolate cloud shadows beyond tile boundary?

[j08lue]

We use Fmask to process multiple adjacent Sentinel 2 tiles. When there are shadows that would go outside of the tile boundary, we get edges at the tile boundary, like you can see below (white=clouds, grey=shadows, low Sun angle from south-south-east).

An ideal solution would be that Fmask had an option to extend the bounds of the output mask, such that all shadows are included. So the southern tile in the scene below would extend north and overlap with the northern tile. Then, when merging the tiles, we could take care of the shadows nicely.

If I had access to the code, I'd be happy to help implementing this.

[qsly09]

Now you can download the code. Thank you so much for sharing your idea.

[j08lue]

Thanks @qsly09, that was quick! I guess now I have to keep my promise and help... 😄 I won't be able to do this on my own, though. If anyone can lead the way who knows the code, that would be very much appreciated!

This part looks relevant:

Fmask/MatchCloudShadow.m

Lines 416 to 421 in db9f01f

	% exclude the pixels out of the entire image.
	tmp_ii_obs=tmp_i_obs(out_id==0);
	tmp_jj_obs=tmp_j_obs(out_id==0);
	clear out_id tmp_i_obs tmp_j_obs;
	tmp_id=sub2ind(dim,tmp_ii_obs,tmp_jj_obs); % matched shadow locations
	clear tmp_ii_obs tmp_jj_obs;