From rspiel at gmx.net Mon Nov 10 04:33:43 2025 From: rspiel at gmx.net (Roland Spielhofer) Date: Mon, 10 Nov 2025 12:33:43 +0000 Subject: [pdal] Delete low points below surface Message-ID: An HTML attachment was scrubbed... URL: From brad.chambers at gmail.com Mon Nov 10 05:37:42 2025 From: brad.chambers at gmail.com (Bradley Chambers) Date: Mon, 10 Nov 2025 07:37:42 -0600 Subject: [pdal] Delete low points below surface In-Reply-To: References: Message-ID: I?d be interested to know what ELM parameters you used. It is configurable, though perhaps still difficult to fine tune. On Mon, Nov 10, 2025 at 06:38 Roland Spielhofer via pdal < pdal at lists.osgeo.org> wrote: > Hi, > I am loking for a PDAL pipline to get rid of low lying points. > The point cloud I am working with is very dense and represents the surface > of a concrete pavement. > The slabs of the pavement are divided by joints - and the points lying in > these joints just below the surface I want to get rid of. > > I created some images showing details of one joint: > https://imgur.com/a/oX7dZcE > > The surface is very flat, and the point density is ~ 5 mm in transversal > and 20 mm in longitudinal direction (=driving direction). > The joints have a depth of ~40 mm (see images). > > I tried out the elm filter, but I guess that the relative z-difference > between the points is too little to mark them as noise. > > Any idea to filter the points in the joint with PDAL would be appreciated > (I can also provide the LAZ pointcloud itself for experiments). > > Thanks in advance and best regards, > Roland > _______________________________________________ > pdal mailing list > pdal at lists.osgeo.org > https://lists.osgeo.org/mailman/listinfo/pdal > -------------- next part -------------- An HTML attachment was scrubbed... URL: From rspiel at gmx.net Mon Nov 10 05:54:23 2025 From: rspiel at gmx.net (Roland Spielhofer) Date: Mon, 10 Nov 2025 13:54:23 +0000 Subject: [pdal] Delete low points below surface In-Reply-To: References: Message-ID: An HTML attachment was scrubbed... URL: From howard at hobu.co Tue Nov 11 19:42:44 2025 From: howard at hobu.co (Howard Butler) Date: Tue, 11 Nov 2025 21:42:44 -0600 Subject: [pdal] Delete low points below surface In-Reply-To: References: Message-ID: It would be slow to compute, but one thought is if you had an additional characterization from filters.covariancefeatures https://pdal.io/en/stable/stages/filters.covariancefeatures.html you could craft a filters.expression that that uses those attributes to help you identify the "linear tunnels". > On Nov 10, 2025, at 7:54?AM, Roland Spielhofer via pdal wrote: > > Hi, > I tried cell = 0.02 - 0.04 and thresholds of 0.001 to 0.01. > In the second image it is quite good to see that the sinusoidal line of points is quite dense in z-direction and I guess that is the problem that the threshold does not work well. It must be quite small, but larger than the variance in the surface. > > In the meantime I also tried this: > > { > "type": "filters.gridDecimation", > "output_type":"max", > "resolution": "0.03", > "value":"Classification=9" > }, > > Keep only the highest of a grid cell - with resolution of 0.03 the low points go away, with 0.025 or 0.02 they stay - 0.02 is roughly the distance between the transversal scan lines. Hoewever, it decimates the concrete surface as well by a mangitude, which I would try to avoid. > > Regards, > Roland > Gesendet: Montag, 10. November 2025 um 14:37 > Von: "Bradley Chambers" > An: "Roland Spielhofer" > CC: pdal at lists.osgeo.org > Betreff: Re: [pdal] Delete low points below surface > I?d be interested to know what ELM parameters you used. It is configurable, though perhaps still difficult to fine tune. > > On Mon, Nov 10, 2025 at 06:38 Roland Spielhofer via pdal > wrote: >> Hi, >> I am loking for a PDAL pipline to get rid of low lying points. >> The point cloud I am working with is very dense and represents the surface of a concrete pavement. >> The slabs of the pavement are divided by joints - and the points lying in these joints just below the surface I want to get rid of. >> >> I created some images showing details of one joint: >> https://imgur.com/a/oX7dZcE >> >> The surface is very flat, and the point density is ~ 5 mm in transversal and 20 mm in longitudinal direction (=driving direction). >> The joints have a depth of ~40 mm (see images). >> >> I tried out the elm filter, but I guess that the relative z-difference between the points is too little to mark them as noise. >> >> Any idea to filter the points in the joint with PDAL would be appreciated (I can also provide the LAZ pointcloud itself for experiments). >> >> Thanks in advance and best regards, >> Roland >> _______________________________________________ >> pdal mailing list >> pdal at lists.osgeo.org >> https://lists.osgeo.org/mailman/listinfo/pdal > _______________________________________________ > pdal mailing list > pdal at lists.osgeo.org > https://lists.osgeo.org/mailman/listinfo/pdal -------------- next part -------------- An HTML attachment was scrubbed... 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