Point on the 3D Tiles represented by the root transform matrix

CesiumJS
1

I have a 3D Tiles model, which is georeferenced using its root transform matrix. I am trying to figure out which point on the 3D Tiles model is represented by the location in root transform matrix.

I am trying to understand this with a simple glTF model. I have a cube (a glTF model), which has the origin vertex (of its local CRS) as (0, 0, 0). When I tile this glTF model to 3D Tiles and then georeference it, will the origin vertex be at the location specified by the transform matrix?

I am looking for answers with regards to the simple case as well as the generic case (a model that does not have its origin vertex as (0, 0, 0)).

Thank you.

2

How is your 3D Tileset created? If you’re using Cesium ion, this thread has some information on this: How to correctly position 3D models when tiling with Cesium ion. The origin will be re-computed to be the center of the geometry, unless you’re using the REST API, which will retain the origin in the original coordinate system.

3

Thank you for your answer. The 3D Tiles are generated using the 3D Tiles Samples Generator. How is the origin computed in this case?

4

I think this samples generator just outputs the glTF model as-is, so the origin shouldn’t be change: https://github.com/CesiumGS/3d-tiles-validator/blob/bb48cafccd61359ed82e9947a20e339442b539fa/samples-generator/lib/createB3dm.js#L68. Note that this isn’t really tiling the model, just embedding it as a single tile in a 3D Tileset.

5

Thank you for the answer. That really helps.