Hi @Railgun-Misaka ,
Have you looked at the Cesium Tile Excluder? It’s in Level 13 of the Cesium for Unreal Samples, link
I’m guessing it’s not as fine grained as loading from your yellow area, but it might get you closer to what you need.
Unfortunately, Cesium for Unreal does not support GeoJSON files. Vector data presents technical challenges and considerations that we have not had a chance to address.
We’re tracking this feature request on Github here. We’ll be sure to give updates when there is progress on the issue.
If your goal is to simply draw a polygon over the terrain / 3D Tiles surface, the easiest way to do that currently is to use a GIS tool like QGIS to rasterize the GeoJSON to a GeoTIFF, styled however you like. Then upload the GeoTIFF to Cesium ion. From there, you can drape it over terrain in Cesium for Unreal by adding a CesiumIonRasterOverlay to your Cesium3DTileset.