This post provides a nice example of masking with a CesiumPolygonRasterOverlay component:
I would like to track down an example in which a high resolution coastline data source is used to create a mask for CesiumWorldTerrain or similar such that the water surface appearance is customizable, while the CesiumWorldTerrain tiles are leveraged above sea level.
This example shows the effect, however, there are few implementation details:
I’m essentially trying to locate a few worked examples before developing a process for preparing the masked tiles / custom imagery
I’m not aware of any existing examples in Cesium for Unreal.
Do you need to use different terrain sources for land versus water? Or are you just trying to show a nice water effect over the existing geometry in the water areas?
If it’s the latter, my first suggestion would be to rasterize and serve your coastline mask via WMS or TMS, and then use a raster overlay plus a custom material to render water in the masked area.
If it’s the former (custom geometry in the water), I’d suggest creating a separate tileset for the bathymetry by uploading a GeoTIFF or similar to Cesium ion. Then add that as a separate Cesium3DTileset in Cesium for Unreal. To clip away Cesium World Terrain in the water areas, use the same technique as above (a WMS or TMS raster overlay with a high-res mask) but make the custom material discard the water pixels entirely (by setting their opacity mask to 0.0) rather than rendering them with fancy water.
The “Editing Tileset Materials” tutorial is essential reading for either approach: