NAC stereo edges

[Stephen Scheidt]

Oleg and Company,

I'm creating a DTM from NAC, but I keep seeing a terrible edge seam on the "left" side of the image. Have you had this artifact? Is there a way to mitigate it?

parallel_stereo \
-t csm -s nac_map_v3_asp_recommended.stereo \
--alignment-method none \
--corr-seed-mode 1 \
--corr-kernel 9 9 \
--subpixel-mode 2 --subpixel-kernel 21 21 \
--prefilter-mode 2 --prefilter-kernel-width 1.4 \
--median-filter-size 3 \
--rm-cleanup-passes 0 \
--bundle-adjust-prefix adjust/ba \
--processes 8 --threads-multiprocess 8 --threads-singleprocess 8 \
L_mp.tif R_mp.tif L.json R.json output_prefix prior-DEM.tif

[Oleg Alexandrov]

This is a bit odd. One thing you can verify is how the mapprojection DEM behaves there. Maybe it needs to go notably beyond this and be nice and smooth. Our dem_mosaic page has some info about how to extend and smooth such a DEM to make it neat enough. If that's the issue, you will have to re-run mapproject after recreating the DEM.

Then, try using --stereo-algorithm asp_mgm, in case you are not doing that already. Likely you are, as I see --corr-kernel 9 9 which is what usually with that, but you can see what your nac_map_v3_asp_recommended.stereo says. In either case can try --corr-kernel 5 5 to see if at least the problematic ribbon artifact there shrinks.

Then, it is always good to overlay left and right mapprojected images and toggle them on and off. Notable changes are likely not a good thing and may be a sign of disagreement between the images and the DEM you mapproject onto.

Not sure about your other settings. We usually run with defaults and no stereo.default at all, and simply set --stereo-algorithm asp_mgm. 

Any experiments you may want to do to fix this can be done on some cropped clips from L.tif and R.tif.

Note that --subpixel-mode 2 is the slowest we got. Likely with mapprojected images that may be not strictly necessary and --subpixel-mode 9 may give almost as good as results or at least --subpixel-mode 3. But this is a runtime thing, not quality.

Let me know. 

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