More flexible styling for classified point clouds

[lilleyse]

If a point cloud is classified, in that it uses batch ids and has a BATCH_LENGTH, the length of each batch table array is equal to BATCH_LENGTH rather than POINTS_LENGTH. This means it is not possible to support per-point attributes when the point cloud is classified. Styling based on a point's "intensity" or "height" isn't possible.

The change would require marking some batch table properties as per-batch properties and others as per-point properties.

[pjcozzi]

Are you certain this would be part of a MVP 1.0?

If it doesn't affect basically all point cloud styling and can be added in a backwards-compatible way, it should be labeled next to reduce scope.

[lilleyse]

It isn't required for 1.0. Any app can get around this limitation by storing classification as a per-point property, however it's more work to get the same functionality. Probably best to scope for next.

[lilleyse]

See CesiumGS/glTF#1 - per-point and per-group properties can be specified together by using multiple batch tables.

[pjcozzi]

CC CesiumGS/glTF#4

[ptrgags]

This is now possible with the EXT_mesh_features extension for glTF: KhronosGroup/glTF#2082. We allow multiple sets of feature ID attributes. See the Feature ID section of the spec