I am using satellite images to generate DEM, but the result of BM algorithm is better than MGM algorithm for the same data. Does anyone know why?
The following are the results of BM and MGM algorithms respectively.
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Thank you for your quick reply
I think MGM algorithm should be better in theory, but it turns out that the result of MGM algorithm has lost a lot of details, while the result of BM algorithm has been made, so I think the result of BM algorithm is better. And I want the DEM to have a higher resolution, so I'm not using mapproject
And I want the DEM to have a higher resolution, so I'm not using mapproject
--在2022年8月15日星期一 UTC+8 23:46:18<oleg.al...@gmail.com> 写道:It is kind of hard to say that BM is better than MGM. Both have holes, which is very usual in mountainous terrain. You can try, per the doc, to create this DEM (by whichever method), at lower resolution, fill holes in it, mapproject onto it, and redo stereo with mapprojected images. It should close the remaining holes. I will also suggest to hillshade the DEMs and zoom in, to see which method has more detail.On Mon, Aug 15, 2022 at 6:38 AM l pp <pplau...@gmail.com> wrote:hi,I am using satellite images to generate DEM, but the result of BM algorithm is better than MGM algorithm for the same data. Does anyone know why?
The following are the results of BM and MGM algorithms respectively.
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bm:
stereo
-t rpc --alignment-method affineepipolar --stereo-algorithm asp_bm
--subpixel-mode 3 L.tiff R.tiff L.xml R.xml
run/out
point2dem out-PC.tif -o run/out --search-radius-factor 5 --dem-hole-fill-len 500 --nodata-value -9999
mgm:
parallel_stereo
-t rpc --alignment-method local_epipolar --stereo-algorithm asp_mgm
--subpixel-mode 3 L.tiff R.tiff L.xml R.xml
run/out
point2dem out-PC.tif -o run/out --search-radius-factor 5 --dem-hole-fill-len 500 --nodata-value -9999
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On Aug 30, 2022, at 7:54 PM, 'Alexandrov, Oleg (ARC-TI)[KBR Wyle Services, LLC]' via Ames Stereo Pipeline Support <ames-stereo-pi...@googlegroups.com> wrote:
Normally a DEM should not have a lot of holes. I will suggest examine the left and right images. The asm_mgm algorithm is in fact a little to eager to fill in areas, and if even that one leaves holes, that is likely a symptom of something not being right with your dataset.From: ames-stereo-pi...@googlegroups.com <ames-stereo-pi...@googlegroups.com> on behalf of l pp <pplau...@gmail.com>
Sent: Tuesday, August 30, 2022 7:48 PM
To: Ames Stereo Pipeline Support <ames-stereo-pi...@googlegroups.com>
Subject: [EXTERNAL] Re: Bm algorithm has better results than MGM
However, after removing -- search-radius-factor 5 flag, the generated DEM will have a lot of holes.
在2022年8月31日星期三 UTC+8 00:18:45<dsh...@uw.edu> 写道:
I recommend dropping the --search-radius-factor 5 flag as well, as that can effectively “blur” features. Should be plenty of points within the standard 1-pixel radius.
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On Aug 30, 2022, at 6:56 AM, Amaury Dehecq <amaury...@gmail.com> wrote:
Hi,
Ok I see. First of all, it is recommended to use parallel_stereo rather than stereo. I think the latter will be deprecated and does not have all the functionalities of parallel_stereo.
Second, SGM/MGM already contain a subpixel refinment, so it is not a common to use --subpixel-mode 3 with it. I would try removing that argument and leave the default value to see if it solves your issue.
Finally, I see that you used --dem-hole-fill-len in poitn2dem. I would also use the default here (which is no filling) first to get an idea of how the DEMs look like. Maybe your issue is that you have many gaps with MGM and then you are filling them, which could explain why they seem to have a poor resolution.
I would also recommend you to look at the log files generated by stereo and point2dem to check the output.
Amaury
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Thank you all for your advice. I will try your advice.
Is MGM always to be preferred (for quality) or can BM sometimes be better? When I generate a DEM using the standard stereo.default file (using bm) I get better results than with the command from the documentation: parallel_stereo {left} {right} --stereo-algorithm asp_mgm --corr-kernel 5 5 --cost-mode 4 --median-filter-size 3 --texture-smooth-size 11 --texture-smooth-scale 0.13 {resultFolderMGM}
point2dem file-PC.tif
I also tried omitting the median-filter-size, --texture-smooth-size and --texture-smooth-scale but it says in the documentation that these must be disabled manually (how is that done?)
See attached BM_DEM and MGM_DEM
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