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Author Topic: Worse sparse cloud with higher aligment setting.  (Read 13310 times)

Marcel

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Re: Worse sparse cloud with higher aligment setting.
« Reply #15 on: June 13, 2014, 03:14:17 PM »
Quote from: Porly link=topic=2489.msg13265#msg13265

As I already said, the reliability of matches between photos in case of 20k could be higher, so that a threshold value between valid/invalid matches in case of lower amount of points could cause a more robust solution.

That would mean that when extracting points, Photoscan somehow makes an assessment of the quality of a point (and only uses the best points). Perhaps Alexey can tell if this is the case?

James

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Re: Worse sparse cloud with higher aligment setting.
« Reply #16 on: June 13, 2014, 04:34:57 PM »
I'm fairly sure that would be the case.

From what I've read in Luhmann (2011), what we're talking about is 'interest operators'. Little algorithms that calculate the interest value of tiny areas of the image based on different criteria such as local contrast, uniqueness within the image, and a whole bunch of other things to do with ensuring that they are good candidates for matching.

Then you set a threshold value to determine which are not interesting enough to bother with, and in the case of photoscan set an upper limit on how many to choose, presumably taking that number from the top of the pile in terms of 'interest'.

As always I'm just guessing and not really adding much :)

Luhmann, Thomas; Robson, Kyle, Harley (2011). Close Range Photogrammetry: Principles, Methods and Applications. Dunbeath,Scotland: Whittles Publishing.

Lambo

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Re: Worse sparse cloud with higher aligment setting.
« Reply #17 on: June 16, 2014, 08:57:09 PM »
So then if that is the case, a good way to test it would be to do a scan with 40K point limit, then use the gradual selection to weed out the bad points to a level roughly the same amount you get with the 20K point limit and then keep going from there and see if you get the same results.
Leo

Marcel

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Re: Worse sparse cloud with higher aligment setting.
« Reply #18 on: June 18, 2014, 05:21:19 AM »
You would need to run Optimize Alignment (Pro version only).  Just deleting bad points has no influence as the camera position would be the same.