[Fix] Add a file and instructions to fix the Lyft dataset (#546)

* Add Lyft fixer file and instructions

* Restore Lyft split files

docs/data_preparation.md

@@ -115,9 +115,10 @@ Download Lyft 3D detection data [HERE](https://www.kaggle.com/c/3d-object-detect
 
 ```bash
 python tools/create_data.py lyft --root-path ./data/lyft --out-dir ./data/lyft --extra-tag lyft --version v1.01
+python tools/data_converter/lyft_data_fixer.py --version v1.01 --root-folder ./data/lyft
 ```
 
-Note that we follow the original folder names for clear organization. Please rename the raw folders as shown above.
+Note that we follow the original folder names for clear organization. Please rename the raw folders as shown above. Also note that the second command serves the purpose of fixing a corrupted lidar data file. Please refer to the discussion [here](https://www.kaggle.com/c/3d-object-detection-for-autonomous-vehicles/discussion/110000) for more details.
 
 ### S3DIS, ScanNet and SUN RGB-D
 

tools/data_converter/lyft_data_fixer.py

+import argparse
+import numpy as np
+import os
+
+
+def fix_lyft(root_folder='./data/lyft', version='v1.01'):
+    # refer to https://www.kaggle.com/c/3d-object-detection-for-autonomous-vehicles/discussion/110000  # noqa
+    lidar_path = 'lidar/host-a011_lidar1_1233090652702363606.bin'
+    root_folder = os.path.join(root_folder, f'{version}-train')
+    lidar_path = os.path.join(root_folder, lidar_path)
+    assert os.path.isfile(lidar_path), f'Please download the complete Lyft ' \
+        f'dataset and make sure {lidar_path} is present.'
+    points = np.fromfile(lidar_path, dtype=np.float32, count=-1)
+    try:
+        points.reshape([-1, 5])
+        print(f'This fix is not required for version {version}.')
+    except ValueError:
+        new_points = np.array(list(points) + [100.0, 1.0], dtype='float32')
+        new_points.tofile(lidar_path)
+        print(f'Appended 100.0 and 1.0 to the end of {lidar_path}.')
+
+
+parser = argparse.ArgumentParser(description='Lyft dataset fixer arg parser')
+parser.add_argument(
+    '--root-folder',
+    type=str,
+    default='./data/lyft',
+    help='specify the root path of Lyft dataset')
+parser.add_argument(
+    '--version',
+    type=str,
+    default='v1.01',
+    help='specify Lyft dataset version')
+args = parser.parse_args()
+
+if __name__ == '__main__':
+    fix_lyft(root_folder=args.root_folder, version=args.version)