what kind of coordinate system should gltf use in b3dm?

CesiumJS
1

Hello Cesium Team,
  These days I tried to make a test with 3D tiles functionality in Cesium. I noticed 3D tile specification is still in progress and b3dm creation tool is unavailable yet. So I want to create B3DM files on my own. But the online B3DM ReadMe.md doesn't explain what difference between binary glTF in B3DM and normal binary glTF is. I knew normal glTF use meter as its length unit. So my question is that how Cesium places these models in right position without matrix information.
  Secondly, the ReadMe say "each vertex has a batchId attribute indicating the model to which it belongs". But normally glTF files use binary buffer to store vertice. How can I add these attributes into binary buffer? Please give me a glTF example file and tell me a method to do it.

Thanks you in advance!

Glen

2

Hi Glen,

if you want to load a .b3dm file with 3D Tiles in Cesium, the vertex coordinates have to be in ECEF.

You need to add the batchIDs (each one is an unsigned short) to the binary Buffer like the vertex data and add an accessor to access it.

Here are the sample models:

https://github.com/AnalyticalGraphicsInc/cesium/tree/3d-tiles/Specs/Data/Cesium3DTiles/Batched/BatchedWithBatchTable

But to test your b3dm you don’t need to add a batch table and batchIDs.

I hope this helps.

Benjamin