**Plese first change the parameters in the launch file for your car**
```bash
roslaunch velodyne start_velodyne.launch
# or
bash /apollo/scripts/velodyne.sh
```
### Export pcd
**Plese first change the parameters in the launch file for your car**
Default export directory: /apollo/data/pcd
```bash
roslaunch velodyne export_pcd.launch
```
motion compensator depends tf2, so gnss_deriver should avaliable too.
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### velodyne Data Validation
```bash
roslaunch velodyne velodyne_check.launch
```
In directory `/apollo/data/log/`, two files are generated by velodyne driver: `velodyne_hz.yyyy-mm-dd-HH-MM-SS.log` and `velodyne_hz.yyyy-mm-dd-HH-MM-SS.log.err` The `.log` file records the time interval and frequency between each frame of compensated point cloud. The `.log.err` file reocrds the timestamp and time interval of the point cloud whose frequency is lower than 9Hz.
### FAQ
1. velodyne port 2368 poll() timeout
The network between the host and velodyne is having problem. Please use `sudo tcpdump -i eth0 udp port 2368` to check if velodyne packets are received.
2. cannot find transform ...
`Compensaton` relies on `tf`, please double check if `gnss_driver` has been started, and also use `rostopic echo /tf` to check if there are any message in the tf.