[pdal] filtering duplicate points

[Andrew Bell]

filters.sample works in 3D.  I'm not sure about the difference you're
seeing.  I don't know what cloud compare is doing.  You're welcome to
submit a bug report if you have some data that you think isn't being
handled properly.

On Mon, May 13, 2019 at 8:56 AM Andrew Cunliffe <andrewmcunliffe at gmail.com>
wrote:

> Thanks for the suggestion Mike,
>
> I just tried running
>                         {
>                             "type": "filters.sample",
>                             "radius": 0.001
>                         },
> on a test cloud with n = 6650 points. With a 0.001 m threshold
> CloudCompare removes 1782 as duplicates (ca. 27%), and makes no visible
> difference to the displayed cloud, so the points removed appear genuine.
> However, with the above parameters, this PDAL pipeline only removes 6
> duplicates.
>
> I wondered whether filters.sample perhaps only considers proximity in XY
> space? (this isn't currently specified in the documentation
> <https://pdal.io/stages/filters.sample.html>). Apologies if I have missed
> something simple, I'm still learning PDAL, but I like it.
>
> Thanks,
> Andy
>
>
>
> On Mon, 13 May 2019 at 13:26, Michael Smith <michael.smith.erdc at gmail.com>
> wrote:
>
>> Andrew,
>>
>>
>>
>> You can use filters.sample and just set a small radius.
>>
>>
>>
>> Mike
>>
>>
>>
>>
>>
>> --
>>
>> Michael Smith
>>
>> Remote Sensing/GIS Center
>>
>> US Army Corps of Engineers
>>
>>
>>
>>
>>
>> *From: *pdal <pdal-bounces at lists.osgeo.org> on behalf of Andrew Cunliffe
>> <andrewmcunliffe at gmail.com>
>> *Date: *Monday, May 13, 2019 at 8:21 AM
>> *To: *PDAL Mailing List <pdal at lists.osgeo.org>
>> *Subject: *[pdal] filtering duplicate points
>>
>>
>>
>> Dear all,
>>
>>
>>
>> I am hoping someone might be able to help me to use PDAL to filter for
>> duplicate points in a point cloud.
>>
>>
>>
>> By duplicate, I mean points that are less than a threshold distance (e.g.
>> 0.001 m) from other points in the cloud. I'm working with
>> photogrammetrically-generated point clouds, in some cases ca. 20-30% of the
>> points are 'duplicates' so removing these has some big benefits later in
>> the pipeline.
>>
>>
>>
>> I'm looking for a filter that functions like 'Remove duplicate points
>> <https://www.cloudcompare.org/doc/wiki/index.php?title=Remove_duplicate_points>'
>> in CloudCompare. I wasn't able to see anything suitable under the filters >
>> cull documentation, unless filters.voxelcenternearestneighbor would
>> achieve this with cell set to 0.001?
>>
>>
>>
>> If anyone else thinks that a filter.duplicate function might be helpful,
>> I'm happy to submit a feature request via Github.
>>
>>
>>
>> Thanks
>>
>> Andy
>>
>>
>> --
>>
>> Dr Andrew Cunliffe
>>
>> Research Fellow
>> School of Geography
>> University of Exeter
>>
>>
>>
>> _______________________________________________ pdal mailing list
>> pdal at lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/pdal
>>
>
>
> --
> Dr Andrew Cunliffe
>
> Research Fellow in Dryland Carbon Dynamics
> School of Geography, College of Life and Environmental Science,
> University of Exeter
>
> UoEx Profile
> <http://geography.exeter.ac.uk/staff/index.php?web_id=Andy_cunliffe>
> Google Scholar
> <https://scholar.google.co.uk/citations?user=GEfm3PIAAAAJ&hl=en>
>
> _______________________________________________
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-- 
Andrew Bell
andrew.bell.ia at gmail.com
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