Update README.md

Author: gitouni

README.md

@@ -22,5 +22,33 @@ More recent version would be OK.
   <summary>TroubleShooting</summary>
   If you have installed g2o through ROS (if you have ROS packages like `base_local_planner`/`teb_local_planner`/`mpc_local_planner`), please exclude it from    LD_LIBRARY_PATH environment variable, or `source config/settings.sh`. </details>
 * For performance, build/rebuild g2o with CMake flag `-DG2O_USE_OPENMP=ON`. See [here](https://github.com/RainerKuemmerle/g2o/issues/689#issuecomment-1565658030).
-# How to Use
-## Step 1
+## Step 1: Estimate Camera and Lidar Poses
+### orb_slam
+an example command for KITTI 04 Sequence:
+```
+./orb_store ../data/04/ ../config/orb_ori/KITTI04-12.yaml ../data/Vocabulary/ORBvoc.txt ../KITTI-04/slam_res/Twc.txt ../KITTI-04/KeyFrames/ ../KITTI-04/Map.yml 1.5
+```
+* `../data/04/`: sequence directory of KITTI Sequence 04
+* `../config/orb_ori/KITTI04-12.yaml`: yaml file for ORB_SLAM
+* `../data/Vocabulary/ORBvoc.txt`: DBoW2 Vocabulary txt file for ORB_SLAM
+* `../KITTI-04/slam_res/Twc.txt`: KeyFrame poses saved by ORB_SLAM, in KITTI format
+* ```../KITTI-04/KeyFrames/```: KeyFrame information saved by ORB_SLAM, can be restored during runtime
+* ```../KITTI-04/Map.yml```: Map saved by ORB_SLAM, can be restored during runtime
+* ```1.5```: Slow Rate of ORB_SLAM2. Duration between Frames: computation + wait_time >= 1.5 * real timestamp
+### F-LOAM
+an example command for KITTI 04 Sequence:
+```
+./floam_run ../data/04/velodyne/ ../KITTI-04/slam_res/floam_raw_04.txt
+```
+* ```../data/04/velodyne/```: directory containing the Lidar PointClouds, whose filenames must be sorted by timestamp.
+* ```../KITTI-04/slam_res/floam_raw_04.txt```: Lidar Poses Estimated by F-LOAM. 
+<details><summary>Note</summary>Note that the number of Lidar Poses is not equal to Camera poses because ORB_SLAM only saved KeyFrame Poses. However, the File Id (FrameId) of these KeyFrames are saved to 'FrameId.yml' in the same directory of 'Map.yml'</details>
+
+### F-LOAM Backend Optimization
+an example command for KITTI 04 Sequence:
+```
+ ./floam_backend ../config/loam/backend.yml ../KITTI-04/slam_res/floam_raw_08.txt ../data/04/velodyne/
+ ```
+ * ```../config/loam/backend.yml```: config file of backend optimzation
+ * ```../KITTI-04/slam_res/floam_raw_08.txt```: Lidar poses estimated by F-LOAM
+ * ```../data/04/velodyne/```: directory containing the Lidar PointClouds, whose filenames must be sorted by timestamp.