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Author Topic: Filtering Sparse Point Cloud  (Read 2255 times)

LFSantosgeo

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Filtering Sparse Point Cloud
« on: May 16, 2018, 07:32:34 PM »
Hello! Is there a consensus about the gradual selection and build points to filter reprojection error of the sparse point cloud?

I've checked the following topics from which I extracted some quotes bellow:
http://www.agisoft.com/forum/index.php?topic=6287.0
http://www.agisoft.com/forum/index.php?topic=8140.0

Quote
GUI: Gradual Selection=X is not the same as buildPoints(error=X)
So they are not the same. And they are not equivalent for the filtering task. What's the difference?

For buildPoints() -- Build Points.
Code: [Select]
buildPoints(error=10[, min_image ][, progress])
Rebuild point cloud for the chunk.
Parameters
• error (float) – Reprojection error threshold.
• min_image (int) – Minimum number of point projections.
• progress (Callable[[float], None]) – Progress callback.

Quote
The perk of using this [buildPoints], apart from that it's shorter, is that statistical 'outliers' that were removed in previous stages could be reinstated if their errors are reduced to within the threshold.

As for the PointCloud.Filter()  -- Gradual Selection:
Code: [Select]
threshold = 0.5
>>> f = PhotoScan.PointCloud.Filter()
>>> f.init(chunk, criterion = PhotoScan.PointCloud.Filter.ReprojectionError)
>>> f.selectPoints(threshold)

Quote
I understand that all matches ,even filtered ones, are kept within the database which means that chunk.buildPoints(error=X) {'coordinates applied...'} will 'resuscitate' some of them and is by no means equivalent to Gradual Selection:Reprojection Error





Luiz Fernando