add kitti_utils.py for evaluating with KITTI metrics (#374)

* add kitti_utils.py for evaluating with KITTI metrics

pcdet/datasets/kitti/kitti_utils.py

@@ -0,0 +1,44 @@
+import numpy as np
+from ...utils import box_utils
+
+
+def transform_annotations_to_kitti_format(annos, map_name_to_kitti=None, info_with_fakelidar=False):
+    """
+    Args:
+        annos:
+        map_name_to_kitti: dict, map name to KITTI names (Car, Pedestrian, Cyclist)
+        info_with_fakelidar:
+    Returns:
+
+    """
+    for anno in annos:
+        for k in range(anno['name'].shape[0]):
+            anno['name'][k] = map_name_to_kitti[anno['name'][k]]
+
+        anno['bbox'] = np.zeros((len(anno['name']), 4))
+        anno['bbox'][:, 2:4] = 50  # [0, 0, 50, 50]
+        anno['truncated'] = np.zeros(len(anno['name']))
+        anno['occluded'] = np.zeros(len(anno['name']))
+        if 'boxes_lidar' in anno:
+            gt_boxes_lidar = anno['boxes_lidar'].copy()
+        else:
+            gt_boxes_lidar = anno['gt_boxes_lidar'].copy()
+
+        if len(gt_boxes_lidar) > 0:
+            if info_with_fakelidar:
+                gt_boxes_lidar = box_utils.boxes3d_kitti_fakelidar_to_lidar(gt_boxes_lidar)
+
+            gt_boxes_lidar[:, 2] -= gt_boxes_lidar[:, 5] / 2
+            anno['location'] = np.zeros((gt_boxes_lidar.shape[0], 3))
+            anno['location'][:, 0] = -gt_boxes_lidar[:, 1]  # x = -y_lidar
+            anno['location'][:, 1] = -gt_boxes_lidar[:, 2]  # y = -z_lidar
+            anno['location'][:, 2] = gt_boxes_lidar[:, 0]  # z = x_lidar
+            dxdydz = gt_boxes_lidar[:, 3:6]
+            anno['dimensions'] = dxdydz[:, [0, 2, 1]]  # lwh ==> lhw
+            anno['rotation_y'] = -gt_boxes_lidar[:, 6] - np.pi / 2.0
+            anno['alpha'] = -np.arctan2(-gt_boxes_lidar[:, 1], gt_boxes_lidar[:, 0]) + anno['rotation_y']
+        else:
+            anno['location'] = anno['dimensions'] = np.zeros((0, 3))
+            anno['rotation_y'] = anno['alpha'] = np.zeros(0)
+
+    return annos