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Author Topic: Photo Align unstable? Has the bug mentioned in the post been fixed?  (Read 3424 times)

PatrickSirk

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I am really having trouble getting my photos (80 photos) to align consistently.  The problem I encounter is that the process reaches a certain point successfully, but then it just fails for the remainder of every image.  I have tried the "tie points" value adjustment and realign camera but to no avail.

As mentioned in other posts, if I (as a test), reopen my file and choose a selection of the photos that did not align previously and only choose that selection, the photos can align properly.  Ugh.

I feel my photo coverage is quite good on the boulder I am shooting. Lots of overlap.  There are some portions of the photos that are out of focus but I seem to cover those areas in subsequent shots where they are in focus. 

My image quality is at .75 or above for each photo.

If there is a method to alleviate this problem, it would be appreciated to have a step by step solve provided. Maybe my coverage is still not good enough?  And I am masking unwanted background in my photos.

Thanks,
Patrick Sirk

bigben

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Re: Photo Align unstable? Has the bug mentioned in the post been fixed?
« Reply #1 on: December 31, 2015, 10:21:35 AM »
I don't know about unstable, but I have noticed a few odd failures that I've attributed to various aspects of the image sequence.  Taking these into consideration on subsequent shoots has provided much more reliable alignment.

  • I have experienced total failure of the intial alignment when the first few images did not contain any overlap between them but did have substantial overlap with many images later in the sequence. Theoretically this shouldn't be a problem, but ensuring that the first few images contain a lot of overlap avoids this.
  • Normally I shoot in such a way that each image overlaps the previous one, but occasionally I'll move to another part of the scene and start shooting again, creating a gap in "continuity".  If the second sequence does not overlap any of the previous image sequence (with images later in the sequence providing overlap) this may cause the alignment to fail either for this second sequence or from this point onwards through the entire project...  Again, theoretically this shouldn't be a problem, but making sure that first few images of the new image sequence overlaps the previous image set seems to avoid this scenario.
  • Significant jumps in GSD can result in the failure of individual images to align

In your case you mention regions of the images being out of focus. This may result in inadequate overlap between images locally within the sequence which may flow on to the rest of the sequence.  Manually aligning them afterwards often works but in some cases the alignment may be off so it pays to check the pointcloud where the new images have been aligned. 

For boulders, I'd only mask out the sky if visible.  Extra background detail may provide the tie points you need to align the images with out of focus sections.

This point cloud (http://files.digitisation.unimelb.edu.au/potree/pointclouds/ricketts-test2.html) was processed with a single alignment step with only one image failing to align (turned out to be motion blur)...  but then I also use a full frame fisheye which provides ample overlap ;)

Artisan S

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Re: Photo Align unstable? Has the bug mentioned in the post been fixed?
« Reply #2 on: December 31, 2015, 11:23:59 AM »
I've either been amazed about the abilities of Agisoft to align photo's and been frustrated about it's unabilities....when I can I shoot concentric circles around the object, either using the turntable method or not....depending on the object's size. I've noticed that overlap is important but Agisoft has had some problems with:

1) Chunks.....individually alligned chunks did not have the same scale meaning reshoot please...this could be my error hard to tell, and personally I'm solution oriented in my work approach, meaning that I don't linger on checking the why but focus on prevention in the future....I standardised my shooting approach as much as possible (see above).

2) Infil shots.....when you have a complex model (lets say a Matchbox Model truck) I like to take infil shots to pay extra attention on certain sight lines I would be missing in the concentric circles, well this seems to baffle Agisoft sometimes. So I stopped bothering with these....Agisoft has it's own logic for filling in holes, and it means that even with smal details caught (and masked out) I can still be confronted with some unwanted action form Agisoft.

3) Mask. I always mask, you means always, like in always? Yes.....always. I know it sucks and it's feels like real work, but it improves allignment and improves scans.  Especially white sky, blue sky and trees in front of buildings, waving trees are the arch enemy of any Agisoft scanner. So mask them out and shoot around them.....it will improve alignment. If can get behind them, if not well you're gonna end up with a partially wavy scan or a scan with some ugly holes.

4) Depth of field....aperture 22 is minimum for shooting macro (and a APS-H or C sensor is preferred over a FF) since DOF is bigger.

5) Don't use flash....unless you know what your doing. I use a ringflash (idea of a german paleontologist and those people are never wrong about anything :-)). Keep the ligth as even a possible, use a tripod and if needed one ore two fill in flashes just to white out the background. Then Magic Wand selection in masking is a breeze....

Does this get 100% predictable results, no. there are still nasty and wonderfull supprises. Like thos bottle opener....tried it with laser, no scan, tried it using SLS no allignment between back and front. With Agisoft first time right.

Greets, Ed.

 

PatrickSirk

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Re: Photo Align unstable? Has the bug mentioned in the post been fixed?
« Reply #3 on: January 01, 2016, 03:43:10 AM »
Fantastic.  So many great tips and knowledge from both of you.  I appreciate the thoroughness and thoughtfulness in your feedback.  It is interesting, as you mentioned, the surprises you can experience with the software.

I started another agisoft project with a different set of shots.  The results were amazing.

 I have determined that yes, I simply did not have enough coverage on the boulder.  A bit nerve wracking because I was shooting in a jungle with much sweat and sweat.  I'm glad my other projects are coming out well from the same location.

I do use a battery powered studio strobe bouncing off a large, diffuse reflector. This gives me a broad, even field of light and I am surprised that I don't get too much specular reflection off my subject matter.

Anyway, thanks again.

Pat