Detection eval - Fix bug if first key has no boxes (nutonomy#408)

* Fix bug if first key has no boxes

* Outsource and test _get_box_class_field

* Revert accidentally committed notebook update

python-sdk/nuscenes/eval/common/loaders.py

@@ -214,16 +214,8 @@ def filter_eval_boxes(nusc: NuScenes,
     :param max_dist: Maps the detection name to the eval distance threshold for that class.
     :param verbose: Whether to print to stdout.
     """
-    # Retrieve box type.
-    assert len(eval_boxes.boxes) > 0
-    first_key = list(eval_boxes.boxes.keys())[0]
-    box = eval_boxes.boxes[first_key][0]
-    if isinstance(box, DetectionBox):
-        class_field = 'detection_name'
-    elif isinstance(box, TrackingBox):
-        class_field = 'tracking_name'
-    else:
-        raise Exception('Error: Invalid box type: %s' % box)
+    # Retrieve box type for detectipn/tracking boxes.
+    class_field = _get_box_class_field(eval_boxes)
 
     # Accumulators for number of filtered boxes.
     total, dist_filter, point_filter, bike_rack_filter = 0, 0, 0, 0
@@ -266,3 +258,27 @@ def filter_eval_boxes(nusc: NuScenes,
         print("=> After bike rack filtering: %d" % bike_rack_filter)
 
     return eval_boxes
+
+
+def _get_box_class_field(eval_boxes: EvalBoxes) -> str:
+    """
+    Retrieve the name of the class field in the boxes.
+    This parses through all boxes until it finds a valid box.
+    If there are no valid boxes, this function throws an exception.
+    :param eval_boxes: The EvalBoxes used for evaluation.
+    :return: The name of the class field in the boxes, e.g. detection_name or tracking_name.
+    """
+    assert len(eval_boxes.boxes) > 0
+    box = None
+    for val in eval_boxes.boxes.values():
+        if len(val) > 0:
+            box = val[0]
+            break
+    if isinstance(box, DetectionBox):
+        class_field = 'detection_name'
+    elif isinstance(box, TrackingBox):
+        class_field = 'tracking_name'
+    else:
+        raise Exception('Error: Invalid box type: %s' % box)
+
+    return class_field

python-sdk/nuscenes/eval/detection/tests/test_loader.py

@@ -9,6 +9,7 @@
 from nuscenes.eval.common.data_classes import EvalBoxes
 from nuscenes.eval.common.loaders import filter_eval_boxes
 from nuscenes.eval.detection.data_classes import DetectionBox
+from nuscenes.eval.common.loaders import _get_box_class_field
 
 
 class TestLoader(unittest.TestCase):
@@ -169,6 +170,25 @@ def test_filter_eval_boxes(self):
         self.assertEqual(filtered_boxes.boxes[sample_token][1].ego_dist, 45.0)
         self.assertEqual(filtered_boxes.boxes[sample_token][2].num_pts, 1)
 
+    def test_get_box_class_field(self):
+        eval_boxes = EvalBoxes()
+        box1 = DetectionBox(sample_token='box1',
+                            translation=(683.681, 1592.002, 0.809),
+                            size=(1, 1, 1),
+                            detection_name='bicycle',
+                            ego_translation=(25.0, 0.0, 0.0))
+
+        box2 = DetectionBox(sample_token='box2',
+                            translation=(683.681, 1592.002, 0.809),
+                            size=(1, 1, 1),
+                            detection_name='motorcycle',
+                            ego_translation=(45.0, 0.0, 0.0))
+        eval_boxes.add_boxes('sample1', [])
+        eval_boxes.add_boxes('sample2', [box1, box2])
+
+        class_field = _get_box_class_field(eval_boxes)
+        self.assertEqual(class_field, 'detection_name')
+
 
 if __name__ == '__main__':
     unittest.main()