Center the SVG to the viewport of threejs

diplomacy/animation/simple-test.html

@@ -576,6 +576,16 @@
           }
           // This rotates the SVG the "correct" way round, and scales it down
           group.scale.set(0.5, -0.5, 0.5)
+          // After adding all meshes to the group, update its matrix:
+          group.updateMatrixWorld(true);
+
+          // Compute the bounding box of the group:
+          const box = new THREE.Box3().setFromObject(group);
+          const center = new THREE.Vector3();
+          box.getCenter(center);
+
+          // Offset the group's position by subtracting the center:
+          group.position.sub(center);
 
           scene.add(group);
         },