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Author Topic: About "Build Orthomosaic"  (Read 8175 times)

Thibaud Capra

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About "Build Orthomosaic"
« on: May 04, 2017, 06:25:43 PM »
Hello everyone,

I'm using orthomosaics to texture external DEMs but I have an issue: some details seem to be kept when I'm using the "Mosaic Blending" option. If I use the "Average Blending" one, these details are blended in and are hidden, but I have weird color disparities.

Either way, to have a clean result, I need to either photoshop these tiny details out or correct the color saturation of my image.

Is there any way to have details about how each mode works?

Thanks.
Best regards.
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Thibaud CAPRA
Master Student in Geodetic Engineering, Cartography & Surveying
Master Thesis in Automated Processing of UAV-based Photogrammetric Data (ResearchGate Link)
INSA de Strasbourg, FRANCE
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Alexey Pasumansky

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Re: About "Build Orthomosaic"
« Reply #1 on: May 04, 2017, 06:32:54 PM »
Hello Thibaud,

The options are described in the manual:
Quote
Blending mode
Mosaic (default) - implements approach with data division into several frequency domains
which are blended independently. The highest frequency component is blended along the seamline
only, each further step away from the seamline resulting in a less number of domains being subject
to blending.
Average - uses the weighted average value of all pixels from individual photos.
Disabled - the color value for the pixel is taken from the photo with the camera view being almost
along the normal to the reconstructed surface in that point.

What kind of issues you are observing that need to be cleaned up and in which mode they do appear?
Best regards,
Alexey Pasumansky,
Agisoft LLC

Thibaud Capra

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Re: About "Build Orthomosaic"
« Reply #2 on: May 05, 2017, 10:40:05 AM »
Hello Alexey,

I must've missed it in the manual, my bad.

Using the Mosaic blending, I see people in my orthophotos that are undesirable (leftmost part):



After some editing, I can get pretty decent results:



Using the Average blending, the same people are merely shadows (this area they are pretty static, but in others they are hidden), but I have issues with colors:



Ideally, I'm looking for a mode that'd combine Mosaic and Average to result in what I have after editing the orthophoto in photoshop.
Best regards.
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Thibaud CAPRA
Master Student in Geodetic Engineering, Cartography & Surveying
Master Thesis in Automated Processing of UAV-based Photogrammetric Data (ResearchGate Link)
INSA de Strasbourg, FRANCE
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Alexey Pasumansky

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Re: About "Build Orthomosaic"
« Reply #3 on: May 05, 2017, 11:12:29 AM »
Hello Thibaud,

Maybe you can use Assign Image option to patch the orthomosaic generated using Mosaic Blending mode?
Best regards,
Alexey Pasumansky,
Agisoft LLC

Thibaud Capra

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Re: About "Build Orthomosaic"
« Reply #4 on: May 05, 2017, 11:34:52 AM »
Hello Alexey,

As these orthos are a result from an automated process using Python scripting, we aim at obtaining orthos that look as good as possible fresh out of the pipeline.
We're going for the mosaic blending mode, then a quick editing for now, because it's shorter than average blending mode editing to rectify the color (note that the one I linked had the Color Correction enabled)

Assign Image is also a manual process, am I right?
Another problem, our processing areas are quite small, only small parts of a 75-hectares area covered by 1400 photos at 90m flight height, so seamline editing doesn't work. Any reason for it? Is it because the generated orthomosaic used the bare minimum of photos?

Best regards.
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Thibaud CAPRA
Master Student in Geodetic Engineering, Cartography & Surveying
Master Thesis in Automated Processing of UAV-based Photogrammetric Data (ResearchGate Link)
INSA de Strasbourg, FRANCE
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Alexey Pasumansky

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Re: About "Build Orthomosaic"
« Reply #5 on: May 05, 2017, 11:52:56 AM »
Hello Thibaud,

Another option is to mask the moving objects on the photos prior to the orthomosaic generation.

Assign image can be automated via Python (in version 1.3), but you need to know, which area you need to patch and create or import the polygonal shape there.

As for the not working seamline editing - any additional details that you can provide? What is not working: shape drawing, image selection from the the list, orthomosaic update, export?
Best regards,
Alexey Pasumansky,
Agisoft LLC

Thibaud Capra

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Re: About "Build Orthomosaic"
« Reply #6 on: May 05, 2017, 11:59:14 AM »
Hello Alexey,

I've been thinking about masking, but inspecting 1400 photos is pretty time consuming. Can I generate masks based on color or something similar? Usually these people wear pretty bright colors!

As for the seamline editing, I can draw a polygon, but when it comes to the image selection, I cannot access it whatsoever.
Best regards.
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Thibaud CAPRA
Master Student in Geodetic Engineering, Cartography & Surveying
Master Thesis in Automated Processing of UAV-based Photogrammetric Data (ResearchGate Link)
INSA de Strasbourg, FRANCE
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Alexey Pasumansky

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Re: About "Build Orthomosaic"
« Reply #7 on: May 05, 2017, 12:47:07 PM »
Hello Thibaud,

Script sample for masking by color is available here:
http://wiki.agisoft.com/wiki/Masks_From_Color.py

And regarding the seam line editing, do you have shapes in the chunk referenced in the same coordinate system the orhomosaic is built? You can check it in Chunk Info dialog.
Best regards,
Alexey Pasumansky,
Agisoft LLC

Thibaud Capra

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Re: About "Build Orthomosaic"
« Reply #8 on: May 05, 2017, 12:55:44 PM »
Hello Alexey,

I assume this wonderful script doesn't exist in 1.2.6?

That might be the problem. If I draw my shapes, then convert them to the same coordinates system, would it work? Or do I have to change the projection beforehand?
« Last Edit: May 05, 2017, 03:48:02 PM by Thibaud Capra »
Best regards.
--
Thibaud CAPRA
Master Student in Geodetic Engineering, Cartography & Surveying
Master Thesis in Automated Processing of UAV-based Photogrammetric Data (ResearchGate Link)
INSA de Strasbourg, FRANCE
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Alexey Pasumansky

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Re: About "Build Orthomosaic"
« Reply #9 on: May 05, 2017, 03:55:43 PM »
Hello Alexey,

I assume this wonderful script doesn't exist in 1.2.6?

That might be the problem. If I draw my shapes, then convert them to the same to the same coordinates system, would it work? Or do I have to change the projection beforehand?

You can check wiki history for the older script version:
http://wiki.agisoft.com/w/index.php?title=Masks_From_Color.py&oldid=101

The coordinate system of the shapes is defined when the first shape is drawn. You can remove Shapes folder from the Workspace pane and then draw new shapes.
Best regards,
Alexey Pasumansky,
Agisoft LLC

Thibaud Capra

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Re: About "Build Orthomosaic"
« Reply #10 on: May 05, 2017, 04:28:12 PM »
Hello Alexey,

Thanks for the help, I'll try the 1.1.0 version and see if it works.

Best regards.
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Thibaud CAPRA
Master Student in Geodetic Engineering, Cartography & Surveying
Master Thesis in Automated Processing of UAV-based Photogrammetric Data (ResearchGate Link)
INSA de Strasbourg, FRANCE
--