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Author Topic: Sparse Cloud: very few Points  (Read 14566 times)

holgar

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Sparse Cloud: very few Points
« on: February 12, 2015, 02:36:18 PM »
Hello Agisoft Community,
I have found a pretty cool Object which I want to Scan. It is a burned out Carwreck.
So I waited for the best weather conditions with a cloudy sky and took the photos.
I made 700 Images with 21 Mpixel with my Canon 5DII.

The Images are very sharp and have good quality. Now I run the Alignment and all Cameras aligned fine.
I used the default settings for Keypointlimit of 40k. This morning I checked the result and I am suprprised I got only 12K points in my sparse clould. After doing some filtering I ended up with 1700 Points.

I would have expected much more points with 700 Cameras. Each camera should find 40K Points.

Before I start the Densecloud calculation I would like to ask you if I should try another Alginment with a higher Keypointlimit.  I fear my sparsecloud is way to small.









Alexey Pasumansky

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Re: Sparse Cloud: very few Points
« Reply #1 on: February 12, 2015, 02:52:27 PM »
Hello Holger,

And what tie-point limit are you using?
Best regards,
Alexey Pasumansky,
Agisoft LLC

holgar

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Re: Sparse Cloud: very few Points
« Reply #2 on: February 12, 2015, 03:10:26 PM »
I left the Tiepoint limit on 1000.

Alexey Pasumansky

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Re: Sparse Cloud: very few Points
« Reply #3 on: February 12, 2015, 03:17:50 PM »
So it might be the reason, why the cloud is so sparse. Each image will have not more than 1000 matching points projections.

If you have time for that you can try to realign the set of images with zero tie-point limit.
Best regards,
Alexey Pasumansky,
Agisoft LLC

holgar

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Re: Sparse Cloud: very few Points
« Reply #4 on: February 12, 2015, 03:25:19 PM »
Thanks for your answer.
I will defenetly do another Alignment. I will try zero tiepont-limit.

Just for my Understanding:
I thought the white dots in the Image-View are Keypoints and the Blue Dots are Tiepoints?
But if that is correct I wonder why I have so few Blue Points? I have like only 10 - 20 Blue Points on each Photo.
What is a good number to have per Image?


holgar

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Re: Sparse Cloud: very few Points
« Reply #5 on: February 12, 2015, 03:29:18 PM »
Do you think 40K is a good vallue for Keypoint limit in my case?
Should I try 40K for Keypoints and Zero for Tiepoints?

Alexey Pasumansky

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Re: Sparse Cloud: very few Points
« Reply #6 on: February 12, 2015, 03:32:59 PM »
Hello Holger,

Actually both white and blue dots are tie-points. Blue - used for alignment (valid), white - unused (invalid). Sparse cloud consists only of "blue" tie-points.

Information about key-points is used during image matching stage and is discarded later.

I can suggest to try 40000 KP and 0 TP (should work similar to the version 1.0).
Best regards,
Alexey Pasumansky,
Agisoft LLC

holgar

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Re: Sparse Cloud: very few Points
« Reply #7 on: February 12, 2015, 03:40:27 PM »
Thanks Alexey, Now I understand better. I will do another Alignment. This will take much longer with TP set to Zero, right?

igor73

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Re: Sparse Cloud: very few Points
« Reply #8 on: February 12, 2015, 05:49:06 PM »
Why the  concern about the sparse cloud?  With the later versions i was also surprised with very low density in the sparse cloud but once you run dense cloud you get a very dense point cloud.  Maybe try to generate dense cloud before aligning again?  Might save you some time.  I also use 1000 tie points and 40 000 point limit. 

Alexey,  will setting the tie point limit to 0 give denser dense clouds ? 

igor73

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Re: Sparse Cloud: very few Points
« Reply #9 on: February 12, 2015, 05:58:01 PM »
Looking at your image again it looks very sparse indeed .  Select a sample area of around 100 images and run dense cloud of that and see how it will turn out.  This will save you the time processing 700 21 pix images to find out you get bad results.

Would be interesting to see your resells so please share. 

Alexey Pasumansky

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Re: Sparse Cloud: very few Points
« Reply #10 on: February 12, 2015, 06:06:28 PM »
Hello Igor,

Sparse cloud density doesn't have direct influence on the dense cloud.

But depth maps are estimated only for those image pairs that have at least one hundred matching points located inside the bounding box (and there's additional condition, if current image have more than 1000 tie-points with any other image, one hundred threshold mentioned above will be replaced by 10% value of the max. number of matching points between current image and the second one, the pair with the biggest number of tie-points).
Best regards,
Alexey Pasumansky,
Agisoft LLC

holgar

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Re: Sparse Cloud: very few Points
« Reply #11 on: February 12, 2015, 06:07:13 PM »
Thanks for your Reply Igor. Yes I figured out that too. a very sparse Cloud can surly result in a very dense Cloud.
But I am more precupied about the Alignment-Quality. I fear that so few Valid points in the Sparse cloud can lead to not su accurate Alignment/Optimization.

I will for sure share my results here ;-). Its the biggest Project I have done so far.Postprocessing the mesh in Zbrush will be a Challange.

igor73

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Re: Sparse Cloud: very few Points
« Reply #12 on: February 12, 2015, 11:15:41 PM »
Zbrush is awesome for editing scan data so you definitely have chosen a good workflow.   Good luck 

holgar

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Re: Sparse Cloud: very few Points
« Reply #13 on: February 13, 2015, 01:17:43 AM »
Zbrush is awesome for editing scan data so you definitely have chosen a good workflow.   Good luck 

My Goal is to generate a Game-Ready asset with Normal-maps. I hope I can produce a good result. I will keep you informed.


holgar

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Re: Sparse Cloud: very few Points
« Reply #14 on: February 13, 2015, 03:51:07 AM »
I have processed 10 Cameras of my Imageset with the recommended Setting of Zero Tiepoints. Now I am getting very good results. Calculationtimes have increased a lot. I hope I get the 700 Images processed.

But I am very very happy with the result: