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Author Topic: No depth maps for some camera positions  (Read 12127 times)

RalfH

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No depth maps for some camera positions
« on: March 01, 2013, 03:11:56 PM »
I have a problem with a project for which I walked around an object to capture it from all sides. Doing this had the result that some camera positions are "seen" by other cameras. As Alexey told me a while ago, depth maps for these cameras are not computed, and these cameras are not used for dense point cloud or meshed model reconstruction. This is very unfortunate, because I now have a set of photographs showing the object from all sides, but I have an area in my model for which I have no dense point cloud coverage. Does anybody know a way (or a workaround) to force PhotoScan to compute depth maps for all camera positions?

Alexey Pasumansky

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Re: No depth maps for some camera positions
« Reply #1 on: March 01, 2013, 06:05:38 PM »
Hello RalfH,

Such cameras are not completely omitted, only some pairs may be skipped during depth map reconstruction.

However, another possible reason of skipping the depth map reconstruction is insufficient number of matches between images in pair.
Best regards,
Alexey Pasumansky,
Agisoft LLC

RalfH

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Re: No depth maps for some camera positions
« Reply #2 on: March 01, 2013, 08:03:50 PM »
Hello Alexey,

I just checked the number of matches, and it turned out that there are indeed almost no valid matches for these photos (only 1 or 2), but hundreds of invalid matches. Strangely, many matches are in the masked areas - I thought PhotoScan would ignore the masked areas for point matching. It's also strange that the images were aligned without problem if there are only 1 or 2 valid matches. And if I create a new project with almost only those photos for which no depth maps were created, I get a few hundred valid matches, and depth maps are created. So what's going on there?

lunar

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Re: No depth maps for some camera positions
« Reply #3 on: March 24, 2013, 08:03:29 PM »
I have the same issue. -standard 0.9.1
this happens randomly
<generate mesh> stage: arbitrary, smooth, low

first try: 1
second:2

some of "clear" dm are ok now, but not all

no stereo pair preselection, almost perfect fit of sparse pc (few misaligned photos of over 300)




another thing: when i disable all photos, and pick some with valid depth map and then generate mesh with build depth map on - then again some of them  are missing...
« Last Edit: March 25, 2013, 02:37:59 PM by lunar »

andy_s

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Re: No depth maps for some camera positions
« Reply #4 on: March 25, 2013, 11:24:43 AM »
Hello Alexey,

I just checked the number of matches, and it turned out that there are indeed almost no valid matches for these photos (only 1 or 2), but hundreds of invalid matches. Strangely, many matches are in the masked areas - I thought PhotoScan would ignore the masked areas for point matching. It's also strange that the images were aligned without problem if there are only 1 or 2 valid matches. And if I create a new project with almost only those photos for which no depth maps were created, I get a few hundred valid matches, and depth maps are created. So what's going on there?

Seems to be a fundamental issue ? i'd also really appreciate a clearer explanation of what's going on here.

 

TDJ109

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Re: No depth maps for some camera positions
« Reply #5 on: May 29, 2013, 08:23:20 PM »
I am having a similar issue. For instance, for one photo set, Photoscan reproduces the front of the object perfectly, but completely omits the back of the object. When I view the matches, the photos of the backside detect hundreds of "invalid" matches but zero "valid" matches. RalfH/lunar, did you ever reach a resolution for this problem?

RalfH

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Re: No depth maps for some camera positions
« Reply #6 on: May 29, 2013, 10:05:45 PM »
No, still no solution for this problem and still hoping that it will be resolved in a future version of Photoscan.

James

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Re: No depth maps for some camera positions
« Reply #7 on: May 29, 2013, 10:35:29 PM »
Could it be a case of insufficient overlap and/or too much difference in camera orientation.

I.e. photoscan detects hundreds of 'candidate' matches, but can not calculate any transform that results in a good pair of camera positions, because the candidate matches are basically wild shots in the dark and the pair of photos are too just different.

When you look at the matches between a pair of aligned photos you can see there is generally a strong correlation between matches connected with blue lines (valid) and no correlation between matches connected with red lines (invalid).

I don't know the algorithm for sure but I guess that there is an initial pass to detect features at a small scale, then match them between pairs of images without reference to the bigger picture, and finally an iterative process to identify the matches that make sense in terms of a basic camera translation/rotation etc.

If the red lines between your invalid matches look like a caffeine driven attempt at a spider's web then the problem is probably with the photos rather than the software.
« Last Edit: May 29, 2013, 10:37:40 PM by James »

RalfH

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Re: No depth maps for some camera positions
« Reply #8 on: May 29, 2013, 11:04:13 PM »
James, you're right about the process and the lines that show the matches, but I have had projects where arbitrary smaller groups of images (e.g. any 5 neighbouring images from a 50 image project) would align well, but Photoscan would just not align the whole project. So in those cases it wasn't the photographs' fault.

an198317

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Re: No depth maps for some camera positions
« Reply #9 on: May 30, 2013, 02:18:02 AM »
This is a REALLY good post, RalfH!! I am having the similar issue with Photoscan Pro. If you remember the posts I had before, we have a camera setup for taking images for small plants, and the overlap between images are more than 50%.

But the "Align camera" seems to be a little strange to me, that is some time Photoscan can't align images together (the positions are completed wrong), but with the same set of images, Photoscan can align them perfect 2nd time, but it might not be good for 3rd time....

This issue happened to me a lot and seems to be "random". So I really want to know what is causing it and how to fix it.

Nan