Models into 3D Tile are deformed

Cesium ion
1

Hi All,
I’m writing a pipeline which converts into 3D tiles buildings generated by CityEngine (a tool for procedural buildings creation from ESRI).

Input models are GLTB files and all coordinates are expressed into a metric CRS (like UTM for example).

The pipeline converts coordinates to ECEF and recenters each model on its centroid - so coordinates are relative to the center of the object and relatively small ( like in the range [-1000 … 1000]).

When resulting GLTB files are packed into B3DM files, I add an RCT_CENTER properties to the batch table containing the coordinates in ECEF of the center.

I thank, this way, I won’t have any “jittering” of the vertices.

Sadly my models are deformed; they don’t jitter a lot but they don’t look as well than before conversion. A lot of details are slightly randomly moved.

I’m wondering how I could solve this problem ?
Should I use some quantized/normalized coordinates instead of just local-metric-centered coordinates ?

Any help appreciated.
Fred.

2

Hi @ftrastour,

Thank you for the detailed information about your use case. Is there a way that you could send us a sample file where you are seeing this behavior? That would help us as we investigate this. Feel free to email it to me directly at matt.boydsurka@cesium.com.

Thanks,
Matt

3

Hello Fred,

My apologies that it’s taken me a while to get back to you on this. I see the jittered vertices in the tileset that you mentioned. I don’t notice any obvious flaws in the methodology you described, so I have a couple of follow-up questions:

  1. Have you tried tiling the source data using Cesium’s 3D buildings tiler? If so, how do the results compare to your pipeline?
  2. How does each individual glb look after coordinates are converted to ECEF and each model is recentered on its centroid? If you examine that model in Blender, does it look correct? If you tile that model individually, are there any problems?

Thanks,
Matt