Matching Terrain Edge Heights of Cartographic Polygon Cutouts


I am using a cartographic polygon to cut out a small area of land for a new development that needs new roads, parking and landscaping etc. My problem is, how can I match the height of the edges of the Cesium tileset, with my new 3D model so that there are no gaps?

For context: Using UE5.2.1 and SketchUp pro 2023 and importing sketchup model via datasmith into UE5.

I have imported terrain in SketchUp with a Bing maps overlay and both UE5 and sketchup are using the same georeference coords. So, everything is located in the same space and I can work out the x,y coordinates of the cartographic polygon and the site boundary in sketchup so they meet. The trouble is finding the z value, which needs to be from the terrain rather than the polygon.

Unfortunately, the terrain in SketchUp does not match the terrain generated in Cesium/Google. I have tried both the Cesium and Google tilesets in UE5, but obviously SketchUp is using a tileset I do not have access to… Previously I have added in heavy planting to hide seams, or the tilesets match, but there will be no planting in all areas on this occasion.

Short of using the UE5 modelling tooIs to recreate the edges and exporting said mesh to SketchUp (A very time intensive way and not completely accurate), is there any way to export the outline from UE5 as a 3D object, or to extract the z value of the edges of the cut out dataset? Or, is it possible to use any of UE5’s other tools to create such an object suitable for export to other 3D programs?