Include terrain in viewport focus calculation and resolve terrain focus target

src/viewport-three/viewport-focus.ts

@@ -450,6 +450,10 @@ function getSceneFocusTarget(document: SceneDocument): ViewportFocusTarget | nul
     includeBrush(bounds, brush);
   }
 
+  for (const terrain of Object.values(document.terrains)) {
+    includeTerrain(bounds, terrain);
+  }
+
   for (const modelInstance of Object.values(document.modelInstances)) {
     includeModelInstance(bounds, modelInstance, document.assets[modelInstance.assetId]);
   }
@@ -505,6 +509,16 @@ export function resolveViewportFocusTarget(document: SceneDocument, selection: E
     }
   }
 
+  const selectedTerrainId = getSingleSelectedTerrainId(selection);
+
+  if (selectedTerrainId !== null) {
+    const terrain = document.terrains[selectedTerrainId];
+
+    if (terrain !== undefined) {
+      return createTerrainFocusTarget(terrain);
+    }
+  }
+
   const selectedPathPoint = getSingleSelectedPathPoint(selection);
 
   if (selectedPathPoint !== null) {