Fix multisweep dtype (nutonomy#581)

* Fix multisweep dtype

* Add error message

Co-authored-by: Holger Caesar <holger.caesar@motional.com>

python-sdk/nuscenes/utils/data_classes.py

@@ -73,7 +73,7 @@ def from_file_multisweep(cls,
         :return: (all_pc, all_times). The aggregated point cloud and timestamps.
         """
         # Init.
-        points = np.zeros((cls.nbr_dims(), 0))
+        points = np.zeros((cls.nbr_dims(), 0), dtype=np.float32)
         all_pc = cls(points)
         all_times = np.zeros((1, 0))
 
@@ -127,6 +127,9 @@ def from_file_multisweep(cls,
             else:
                 current_sd_rec = nusc.get('sample_data', current_sd_rec['prev'])
 
+        # Check that the multisweep pointcloud has the same dtype as individual pointclouds.
+        assert all_pc.points.dtype == np.float32, 'Error: Invalid dtype for multisweep pointcloud!'
+
         return all_pc, all_times
 
     def nbr_points(self) -> int: