Impossible alignment with repeated wall patterns?
Yeah I have no idea how I can fix this problem... I cant align the cameras at all no matter how many control points..
There are patterns on the wall that repeat like this.. any ideas here?
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Hey Steven,
preselector to 250? Wow. Thanks for this idea. I think that was probably the most important one. Along with the CPs.
Apart from that, you are making a great case about shaking it slightly until everything falls into place. At some point it's more of an intuition than exact sciense.
I'm not so sure how much the white-balance helped. I'm pretty certain that feature detection can deal with different colors - features are more than that. I had no problems with aligning images that were taken at completely different times of the day and even with perfect white balance you could not avoid some changes in color. Same for images with and without flash (murmuring in the background) because in spite of tons of "advice" out there, flash usually works just fine. I think these tips stem from a time when the algorythms were still more error prone and they are also from many scientific sources, where people look more at the numbers than at the real-life results.
Panos:
Shooting several images from one position is not neccessarily impossible. In most cases it will align perfectly well, as long as the other requirements for photogrammetry are upheld. The problem CAN arise when RC picks 2 images from the same position to calculate the depth. RC will still come up with a slight difference for each position, so the base for such a pair is incredibly tiny, which will lead to excessive noise. So it's not that it won't work, but if there aren't enough images for RC to choose from, the quality can go down the tubes. The safest way to avoid trouble (I'm speculating here) is to reduce the overlap in the panos to almost nothing and use a tripod head that has its nodal point significantly off the sensor, so that with each turn the image position also shifts to an extent that is not "dangerous" any more.
Best thread in ages!
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Gotz I agree about the white balance and the sentiments about slight exposure changes. The software can handle a little, but just like changes in position need to be gradual so do these changes.
I also a few idea about how feature detection works. I imagine it uses edge detection. To the RC it probably looks like this
From low detection and few points
to high detection with many detected features
With maybe color Information overlayed Like
And then adjusts the "perspective" or keystone of each image till features start to line up. It's probably smart about the process and starts with the pictures with the most similar features to speed up calculation. This is how I imagine in my head the software works.
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here are all the files I used on this project
https://drive.google.com/open?id=1_CZobR5gCslMfSCRJUKN9P26Luiwh5w8
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Pending again :(
https://drive.google.com/open?id=1TL4kwTp1-GUyVN9c54aRPe5PzgXftWfg -
Hey Steven,
very nice advice and examples! How does the model turn out? The angles between the shots might be a bit large and there should be more shots of the top, but I guess you've left those out...
This st***d approval pending has thwarted me a few times as well. Nice workaround btw. The weird thing is that I get your notifications with the full text anyway! lol
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