Custom Projection

Hi community!

I am processing a batch of data from other projection coordinate systems, and what I know is that Cesium only supports EPSG4326 and EPSG3857, corresponding to GeographicTilingScheme and WebMercatorTilingScheme.

I tried using WebMercatorTilingScheme and was able to successfully load the data, but the position of the data shifted. In this case, can I use the Proj4.js library and modify the project and unproject in WebMercatorProjection to reproject my data to the correct position?