OGC 3D Tiles rendered in UTM coordinate systems rather than ECEF?

The Cesium 3D engine seems to operate with Earth Centred Earth Fixed coordinate system (ECEF - related to the the WGS84 ellipsoid), as the 3d coordinate system that is used for rendering.


Thus Cesium seems to require that 3D tiles must be placed using WGS84.

But what if you wanted the rendering to happen in a coordinate system where for the 3D Tiles were placed on a plane and not around an ellipsoid like in ECEF, thus allowing a vertical axis
to represent height above or below sea-level There are many 3D datasets that are geo-referenced in for instance UTM. And there are certain features that would be easier to implement if you can assume “flat earth” projections

I do belive that the OGC 3D Tiles specification allows for coordinate refernce systems such as UTM but I don´t know of any 3D Tiles rendering engine that has implemented support for it? If someone else knows about one I would love to learn about it!

I would as you might imagine love for Cesium to add support for rendering in a UTM reference frame. Would that be something Cesium would consider implementing?

Best regards,
Jan-Erik Vinje