Make pointcloud attenuation dependent on geometricError/lod-level

[jo-chemla]

Is your feature request related to a problem? Please describe.

Current implementation of the OGC 3Dtiles pointcloud rendering relies on threejs PointsMaterial where a parameter sizeAttenuation specifies whether points' size is attenuated by the camera depth - therefore consist of a switch whether material.pointSize is expressed as pixel screen units or scene world units.

3DTilesRendererJS/src/plugins/three/DebugTilesPlugin.js

Lines 443 to 445 in 8142a2d

	const pointsMaterial = new PointsMaterial();
	pointsMaterial.size = originalMaterial.size;
	pointsMaterial.sizeAttenuation = originalMaterial.sizeAttenuation;

Describe the solution you'd like

For better rendering of multi-resolution pointcloud tilesets, it could be helpful to have that point-size-attenuation be dependent on the geometricError or level of the tile within the hierarchy - the same way it is currently implemented within cesiumjs (+ plugins) or potree:

• cesiumjs PointCloudShading attenuation performs point attenuation based on geometric error, see this useful sandcastle demo
• and potree attenuation where attenuation = 2 ** lod_level.

Describe alternatives you've considered

This would probably involves developing a custom pointcloud shader that would account for point-sizing and attenuation per vertex, given the lod-level passed as uniform.

Additional context

Note another useful feature of the Potree Renderer is HQ Splats rendering, which resembles antialiasing, although done differently - see HQSplatRenderer, main related bits of the vertex-shader and fragement-shader highlighted

[gkjohnson]

Do you have an example of what specifically you're interested in the points behaving like? The Cesium example uses screen-space sizing (PointsMaterial.sizeAttenuation === false) while the potree example(s) use world-space sizing (sizeAttenuation === true). Right now the behavior is left to the default three.js behavior when loading a PNTS or GLTF file with points.

In either case there should be no need for a new shader to scale based on LoD or geometric error. The points material "size" value can be adjusted by a factor based on either tile value. Regarding "HQ splats" from potree - from this issue it seems that the points are just being rendered with the depth of a sphere so the points intersect, though this would require shader modifications.

Either way everything you're suggesting can already be implemented, though, using a plugin or by modifying the tile content geometry using the load-model event.