Improve PLY loading robustness and error handling (#150)

* Improve PLY loading robustness and error handling

- Add support for PLY files with only DC components (no higher-order spherical harmonics)
- Initialize higher-order harmonics to zero when only DC components are available
- Add better error logging with full traceback in ply_to_usd.py script
- Improve error messages for unexpected spherical harmonics data structure

* Update threedgrut/model/model.py

Co-authored-by: Qi Wu <[email protected]>

---------

Co-authored-by: Qi Wu <[email protected]>

Author: Hermanye996

threedgrut/export/scripts/ply_to_usd.py

@@ -98,8 +98,10 @@ def main():
         logger.info(f"Successfully exported to {output_path}")
     except Exception as e:
         logger.error(f"Error processing PLY file: {e}")
+        import traceback
+        logger.error(f"Full traceback: {traceback.format_exc()}")
         sys.exit(1)
 
 
 if __name__ == "__main__":
-    main()
+    main()

threedgrut/model/model.py

@@ -685,12 +685,21 @@ def init_from_ply(self, mogt_path:str, init_model=True):
         extra_f_names = [p.name for p in plydata.elements[0].properties if p.name.startswith("f_rest_")]
         extra_f_names = sorted(extra_f_names, key = lambda x: int(x.split('_')[-1]))
         num_speculars = (self.max_n_features + 1) ** 2 - 1
-        assert len(extra_f_names)==3*num_speculars
-        mogt_specular = np.zeros((num_gaussians, len(extra_f_names)))
-        for idx, attr_name in enumerate(extra_f_names):
-            mogt_specular[:, idx] = np.asarray(plydata.elements[0][attr_name])
-        mogt_specular = mogt_specular.reshape((num_gaussians,3,num_speculars))
-        mogt_specular = mogt_specular.transpose(0, 2, 1).reshape((num_gaussians,num_speculars*3))
+        expected_extra_f_count = 3 * num_speculars
+        
+        mogt_specular = np.zeros((num_gaussians, expected_extra_f_count))
+        if len(extra_f_names) == expected_extra_f_count:
+            # Full spherical harmonics data available
+            for idx, attr_name in enumerate(extra_f_names):
+                mogt_specular[:, idx] = np.asarray(plydata.elements[0][attr_name])
+            mogt_specular = mogt_specular.reshape((num_gaussians,3,num_speculars))
+            mogt_specular = mogt_specular.transpose(0, 2, 1).reshape((num_gaussians,num_speculars*3))
+        elif len(extra_f_names) == 0:
+            # Only DC components available, create zero-filled higher-order harmonics
+            logger.info(f"PLY file only contains DC components, initializing higher-order spherical harmonics to zero")
+        else:
+            # Partial data - this is unexpected
+            raise ValueError(f"Unexpected number of f_rest_ properties: found {len(extra_f_names)}, expected {expected_extra_f_count} or 0")
 
         scale_names = [p.name for p in plydata.elements[0].properties if p.name.startswith("scale_")]
         scale_names = sorted(scale_names, key = lambda x: int(x.split('_')[-1]))