ClippingPlane coordinate system in 3DTilesets

[runeaasgaard]

Feature

As it is today the origin of the ClippingPlane coordinate system for a 3DTileset is set from the center of the boundingsphere of the root tile of the tileset. For a large tileset this can be a rather arbitrary point, not easily related to the individual objects in the tileset and not well known to the client.

The tileset clipping origin transform is also only accessible trough a private and undocumented property of the tileset, and the only way I have found to use my_preferred_clipping_origin_matrix is to set the clipping plane collection modelMatrix to the difference between my matrix and the tileset clippingPlanesOriginMatrix like this:
const scratch_invert = Matrix4(); Cesium.Matrix4.inverse(tileset.clippingPlanesOriginMatrix, scratch_invert); Cesium.Matrix4.multiply(scratch_invert, my_preferred_clipping_origin_matrix, tileset.clippingPlanes.modelMatrix);

If there is a better way I would have liked an example in the ClippingPlaneCollection documentation. If not, I would have liked a possibility to set the tileset clippingPlanesOriginMatrix on tileset creation, using the root tile origin only when this is not provided.
let tileset = await Cesium.Cesium3DTileset.fromUrl( my_tileset_urll, { dynamicScreenSpaceError: true, clippingPlanesOriginMatrix: Matrix4.IDENTITY } );