[pdal] filtering duplicate points

[Andrew Bell]

Andrew,

A look at the cloud compare code suggests it works very differently from
PDAL filters.sample and depends on the way that points are distributed in
an octree.  Rather than checking actual distance, CC tries to remove points
in octree cells, that may be closer than the specified distance, depending
on the octree organization.  You might try setting the distance smaller in
PDAL to see if you get results more to your liking.  (This is based on a
very cursory look at the CC code, so take it with a grain of salt.)

On Mon, May 13, 2019 at 8:59 AM Andrew Bell <andrew.bell.ia at gmail.com>
wrote:

>
> 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>
>>
>> _______________________________________________
>> pdal mailing list
>> pdal at lists.osgeo.org
>> https://lists.osgeo.org/mailman/listinfo/pdal
>
>
>
> --
> Andrew Bell
> andrew.bell.ia at gmail.com
>


-- 
Andrew Bell
andrew.bell.ia at gmail.com
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