lidar camera extrinsic calibration procedure is added.

docs/utlidar-camera-calib.md

@@ -0,0 +1,48 @@
+
+# Lidar to Camera Extrinsic Calibration
+First pull the docker image:
+```bash
+docker pull koide3/direct_visual_lidar_calibration:humble
+```
+Then activate the X server connection port:
+```bash 
+xhost +
+```
+and run the container with GUI support:
+```bash
+docker run \
+  -it \
+  --rm \
+  --net host \
+  --gpus all \
+  -e DISPLAY=$DISPLAY \
+  -v $HOME/.Xauthority:/root/.Xauthority \
+  -v /path/to/input/bags:/tmp/input_bags \
+  -v /path/to/save/result:/tmp/preprocessed \
+  koide3/direct_visual_lidar_calibration:humble 
+```
+
+Inside the container generate images from the LiDAR data (Preprocessing):
+```bash
+ros2 run direct_visual_lidar_calibration preprocess /path/to/bag/dir /path/to/result/dir \
+  --image_topic /camera/color/image_raw \
+  --points_topic /utlidar/cloud \
+  --camera_model plumb_bob \
+  --camera_intrinsics 379.7099304199219,320.3064270019531,379.3695983886719,243.11753845214844 \
+  --camera_distortion_coeffs -0.057967256754636765,0.0704321563243866,-0.00015285948757082224,0.0006057045538909733,-0.022366832941770554
+```
+then manually select the correspondences between the 3D pointcloud and the image:
+
+```bash
+ros2 run direct_visual_lidar_calibration initial_guess_manual /path/to/result/dir
+```
+Finally perform a refinement step by running:
+
+```bash
+ros2 run direct_visual_lidar_calibration calibrate /path/to/result/dir
+```
+[![Alt text](https://img.youtube.com/vi/YOUTUBE_VIDEO_ID/0.jpg)](https://www.youtube.com/watch?v=FTlC9RwEVxY&t=43s)
+
+# Source
+This procedure has been taken from [direct_visual_lidar_calibration toolbox](https://koide3.github.io/direct_visual_lidar_calibration/).
+