2D feature-based alignment of orthophotos using pc_align

[Benjamin Hemingway]

The documentation indicates that pc_align supports feature-based alignment (through hillshading DEMs). Similarly, I would like to align overlapping orthophotos using 2D feature-based alignment. Can this be accomplished in ASP?

[Alexandrov, Oleg (ARC-TI)[KBR Wyle Services, LLC]]

I guess it could. It would interpret each orthophoto as a DEM (if it is a geotiff) with each grayscale value a height, create a hillshaded image from it, find features in those, and align it that way.

Yes, inane this is. Ideally you would want features to be found in othophotos, and not in their hillshaded versions. You can look at how pc_align does its job. First it find matches among hillshaded images, then computes a transform based on them. You could in principle use the same calls to ipfind and ipmatch to find matches between the orthoimages themselves, and then pc_align can be told to use a given match-file you compute via the --match-file option. It would then apply whatever transform it finds onto one orthoimage to bring it on top of another one.

Not sure how it will work, but if you have no better tools you can give it a try. In principle, one could cook up something with python and opencv avoiding ASP altogether. Or maybe somebody already wrote something.

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From: ames-stereo-pi...@googlegroups.com <ames-stereo-pi...@googlegroups.com> on behalf of Benjamin Hemingway <blhe...@asu.edu>
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To: Ames Stereo Pipeline Support <ames-stereo-pi...@googlegroups.com>
Subject: [EXTERNAL] 2D feature-based alignment of orthophotos using pc_align

 

The documentation indicates that pc_align supports feature-based alignment (through hillshading DEMs). Similarly, I would like to align overlapping orthophotos using 2D feature-based alignment. Can this be accomplished in ASP?

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[Benjamin Hemingway]

Thank you, Oleg, for the helpful suggestions. I’ll will give that a shot. 

Best,

Ben

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[Matthieu Volat]

Some time ago, I did this by running ipfind/ipmatch, then using a gdal script to read and insert the matches as GCP and generate a new affine transform I used to resample/rectify one image against another using gdalwarp. I did that with georeferenced images, I guess this could work with non georeferenced dataset by declaring a dummy georef matrix.

The concept kind of worked, my issue was as always to have a robust matching set.

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Matthieu Volat

CNRS/Observatoire de Lyon

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[Shashank Bhushan]

Also, take a look at the package Arosics, which has wrapped up everything mentioned in this discussion above end to end for orthophotos :)

I find the package to be very nice.

https://pypi.org/project/arosics/

https://www.mdpi.com/2072-4292/9/7/676

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[Benjamin Hemingway]

Thank you, Matthieu and Shashank. This is all really helpful. I should be able to accomplish what I am wanting to do. Thanks again.

-Ben

[mikita belikau]

Guys, is there somewhere available source code for this task I can examine?

I want to do exactly the same thing - coregister several HiRISE JP2 (LBL) files. 

So far I have run ipfind/ipmatch which gave me *.match file, but the next steps are a bit fuzzy for me right now.

I understand that I need to perform affine transformation for this file and then somehow use this to create a gcp file and use it in gdal's translate/wrap commands. Is there any source code available in some public repo?

[Oleg Alexandrov]

ASP added support for alignment of images. The documentation is at https://stereopipeline.readthedocs.io/en/latest/tools/image_align.html. The latest build having this functionality is at https://github.com/NeoGeographyToolkit/StereoPipeline/releases.