add clarification for Waymo evaluation (#384)

* bugfixed: add num_points_in_gt to the waymo_infos for evaluation

* add clarification for Waymo evaluation

README.md

@@ -18,6 +18,10 @@ It is also the official code release of [`[PointRCNN]`](https://arxiv.org/abs/18
 
 
 ## Changelog
+[2020-11-27] **Bugfixed:** Please re-prepare the validation infos of Waymo dataset (version 1.2) if you would like to 
+use our provided Waymo evaluation tool (see [PR](https://github.com/open-mmlab/OpenPCDet/pull/383)). 
+Note that you do not need to re-prepare the training data and ground-truth database. 
+
 [2020-11-10] **NEW:** The [Waymo Open Dataset](#waymo-open-dataset-baselines) has been supported with state-of-the-art results. Currently we provide the 
 configs and results of `SECOND`, `PartA2` and `PV-RCNN` on the Waymo Open Dataset, and more models could be easily supported by modifying their dataset configs. 
 

pcdet/datasets/waymo/waymo_eval.py

@@ -46,6 +46,11 @@ class OpenPCDetWaymoDetectionMetricsEstimator(tf.test.TestCase):
                     info['difficulty'][(info['num_points_in_gt'] <= 5) & zero_difficulty_mask] = 2
                     nonzero_mask = info['num_points_in_gt'] > 0
                     box_mask = box_mask & nonzero_mask
+                else:
+                    print('Please provide the num_points_in_gt for evaluating on Waymo Dataset '
+                          '(If you create Waymo Infos before 20201126, please re-create the validation infos '
+                          'with version 1.2 Waymo dataset to get this attribute). SSS of OpenPCDet')
+                    raise NotImplementedError
 
                 num_boxes = box_mask.sum()
                 box_name = info['name'][box_mask]