3d-tiles and curvature of the earth

[ZhouHai]

hi，all

    I would like to ask a question about 3dtiles and the curvature of the earth. I have a railway model that is more than 30 kilometers long. 

    I convert it to 3dtiles and load it into cesium. Due to the influence of the curvature of the earth, the two ends of the model are far away from the earth.

    I saw this post to convert all the tiles, https://groups.google.com/forum/?hl=en#!searchin/cesium-dev/curvature|sort:date/cesium-dev/VG4OpbOoIU0/di6DxVoABgAJ ，but there will be some problems. In some model gaps, there may be some situations. 

    Is there a better solution, such as modifying the coordinate position of each point of the model in the shader according to the curvature, making the whole model look more sleek.

thanks！

[Omar Shehata]

The problem is that when tiling models like this Cesium ion does not currently take into account any projection information. So in this case, the ideal solution is to be able to say that the coordinates of this model are in some specific projection, so the geometry is interpreted to be at a fixed height from the surface as opposed to just an absolute position in space relative to one model origin. 

This is something we're currently working on improving. Can you let me know what the asset ID for this asset is? That'll help us look into making sure we can support use cases like this. 

[ZhouHai]

@Omar Shehata Thanks for your reply, this model is converted locally, not uploaded to cesium ion. Do you think it is more appropriate to process it in the 3dtiles generation stage or in the render stage?

[Omar Shehata]

I think it would make sense to do it while generating the 3D Tiles, that way it can accurately adhere to the surface and still be efficient to render.

[ZhouHai]

I made some attempts to modify the position of each point in the shader program and get the result I want, but I can't modify the bounding box, causing problems with the hiding and selection of the tile, so the processing in the model generation phase is even more Good choice.

在 2019年9月20日星期五 UTC+8下午10:15:41，Omar Shehata写道：