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Author Topic: Align photos point limit  (Read 7866 times)

bmc130

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Align photos point limit
« on: January 08, 2014, 04:33:47 PM »
Can someone please explain to me what this Point limit within advanced in the Align Photos window does. Will I get a better scan/detail if I change it to 80000?

cbnewham

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Re: Align photos point limit
« Reply #1 on: January 08, 2014, 04:46:24 PM »
From what I have seen it is an upper limit to the number of points it will use for finding points and matching them. The number of points you get in total on your photos will depend on the number of places it can find features to generate points for and the number of points in the final sparse cloud (which were matched) will be lower than this.


David Cockey

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Re: Align photos point limit
« Reply #2 on: January 08, 2014, 07:08:09 PM »
The point limit sets the maximum number of points which will be identified in each photo during the Align Photos process. As cbnewham mentioned the number of points actually identified on each photo may be less than the maximum number set.

I have experimented setting the maximum number to 80,000 with High Accuracy when aligning 15Mp photos. I have not seen appreciable difference compared to a limit of 40,000.

With Medium Accuracy only 20,000 points or less are identified in each photo so changing from 40,000 to 80,000 does not make any difference.

 

bmc130

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Re: Align photos point limit
« Reply #3 on: January 08, 2014, 08:35:52 PM »
Ok cool, thanks David Cockey and cbnewham.

David, do you remember how much difference in calculation time was it between the 20, 40 and 80k settings?

Marcel

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Re: Align photos point limit
« Reply #4 on: January 08, 2014, 08:50:17 PM »
With Medium Accuracy only 20,000 points or less are identified in each photo so changing from 40,000 to 80,000 does not make any difference.

I think the Low/Medium/High is setting how much the images are downscaled before points are extracted (just like the accuracy sets image downscaling during Dense Cloud generation). If you change the setting from Medium to High, the number of points increases quadratically.

We hope to do some experimentation on the max number of points in the near future. We'd really like to find out the most effective setting because it can save considerable time. In the meantime I also use 80.000 or 100.000 points just to be sure. Compared to the Dense Cloud generation the Align phase is still pretty fast anyway.

Calculation time can also differ a lot between projects. For example, I currently have a 300 shot project that takes 6+ hours to align. I think it is because it has trouble finding which photos are matching pairs (because photos are very similar), so it has to match almost all points against eachother.