Add method to clear terrain meshes in RuntimeHost

src/runtime-three/runtime-host.ts

@@ -811,6 +811,7 @@ export class RuntimeHost {
     this.resizeObserver = null;
     this.clearLocalLights();
     this.clearBrushMeshes();
+    this.clearTerrainMeshes();
     this.clearModelRenderObjects();
     this.collisionWorldRequestId += 1;
     this.clearCollisionWorld();
@@ -2702,6 +2703,16 @@ export class RuntimeHost {
     this.runtimeWaterContactUniforms.length = 0;
   }
 
+  private clearTerrainMeshes() {
+    for (const mesh of this.terrainMeshes.values()) {
+      this.terrainGroup.remove(mesh);
+      mesh.geometry.dispose();
+      mesh.material.dispose();
+    }
+
+    this.terrainMeshes.clear();
+  }
+
   private disposeUniqueMaterials(materials: Material[]) {
     for (const material of new Set(materials)) {
       material.dispose();