How to use HeightReference with Primitive

CesiumJS
1

As the title，I wanna use polygon primitive with terrain，but there is no HeightReference option.

2

hi if you want to use clampToGround option use viewer.scene.groundPrimitives,
or use geometryInstance like this

 viewer.scene.primitives.add(new Cesium.Primitive({
                geometryInstances : new Cesium.GeometryInstance({
                    geometry : new Cesium.PolygonGeometry({
                        polygonHierarchy : new Cesium.PolygonHierarchy(
                            yourPositionArr 
                        ),
                        extrudedHeight : yourHeight,
                        closeTop : true,
                        closeBottom : true,
                        vertexFormat : Cesium.EllipsoidSurfaceAppearance.VERTEX_FORMAT,
                    }),
                    id : yourId
                }),
                appearance : yourAppearance,
            }));
3

@jhkim0623
I want to correct his height on the terrain, for example, I have a set of polygon coordinates representing buildings, and I want to extruded them to make them look like buildings. I want him to adjust his height based on the terrain to ensure that he doesn’t end up inside mountains or floating above caves.
Thank you very much!

4

about extrudedHeight…
use this code

async getTerrainHeight(lon,lat) {
let cartoLoc = Cesium.Cartographic.fromDegrees(lon,lat);
let terrHgt = 0;
try {
const updatedLocation = await Cesium.sampleTerrainMostDetailed(viewer.terrainProvider,
[cartoLoc]);
terrHgt = updatedLocation[0].height;
return terrHgt;
} catch (error) {
console.error(“Error sampling terrain:”, error);
return 0;
}
},

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