Fix seams/gaps when exporting mesh using marching cubes Fixes #2721 (#3598)

Author: Dawars

nerfstudio/exporter/marching_cubes.py

@@ -251,4 +251,5 @@ def evaluate(points: torch.Tensor) -> torch.Tensor:
                     meshes.append(meshcrop)
 
     combined_mesh: trimesh.Trimesh = trimesh.util.concatenate(meshes)  # type: ignore
+    combined_mesh.merge_vertices(merge_tex=True, merge_norm=True)
     return combined_mesh