[QGIS-Developer] Point cloud renderer: tile borders visible?

[Andreas Neumann]

Hi Martin,

Thanks for the explanation.

I confirm that reducing the maximum error helps to remove the artefacts.
WIth 0.5 mm I could still see them at one particular zoom level, but with
0.4 mm it was completely gone.

Thanks a lot,
Andreas


On Tue, 8 Dec 2020 at 13:15, Martin Dobias <wonder.sk at gmail.com> wrote:

> Hi Andreas
>
> The artifacts you are seeing are caused by the fact how the Entwine tool
> works in the default configuration. When creating the octree index of point
> cloud data, points are organized in a hierarchy of nodes (each containing
> usually tens of thousands of points), with each level of the hierarchy
> having smaller bounding volume and higher density. One optimization that
> Entwine does is that if child nodes contain a small amount of points, they
> get merged into the parent node in the hierarchy - in the hope this will
> lower the number of nodes and therefore also the number of requests that
> need to be done. See Entwine configuration [1] for more details -
> especially the options like minNodeSize, maxNodeSize, overflowDepth,
> overflowThreshold. So the artifacts could be simply fixed by reindexing the
> dataset with modified configuration.
>
> All that said, maybe none of that is necessary:
> 1. I would suggest lowering "Maximum error" in Layer styling to e.g. 0.5
> mm or even 0.3 mm (assuming the default point size of 1mm) - this should be
> giving you a rendering result with very little holes - it is much nicer to
> look at and the artifacts should be gone at all scales  (it will increase
> the rendering time, but I think it is worth it and I think we should lower
> the default maximum error - the higher maximum error was initially used
> mainly as a debugging tool for us to see if the point spacing in the
> rendered map matches the expectations)
> 2. For indexing of point clouds, we will be internally using Untwine [2] -
> a newer approach (also coming from friends at Hobu!) that has different
> configuration and probably won't be showing these artifacts. Peter is
> currently working on the integration [3]
>
> Regards
> Martin
>
> [1] https://entwine.io/configuration.html
> [2] https://github.com/hobu/untwine
> [3] https://github.com/qgis/QGIS/pull/40404
>
>
> On Tue, Dec 8, 2020 at 10:30 AM Andreas Neumann <a.neumann at carto.net>
> wrote:
>
>> Hi,
>>
>> When testing the 2D point cloud renderer I noticed that in certain scales
>> / zoom levels one can clearly see point cloud tile borders:
>>
>> see screenshot at
>> https://www.carto.net/neumann/temp/point_cloud_artefacts.png
>>
>> There seem to be different densities involved in certain regions here,
>> but clearly they correspond to tile borders.
>>
>> Is this an expected artefact? Can this be avoided?
>>
>> When I zoom in or out, these artefacts seem to disappear.
>>
>> Thanks and greetings,
>>
>> Andreas
>>
>>
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-- 

--
Andreas Neumann
QGIS.ORG board member (treasurer)
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