VLP16-HiRes doubled lines in cloud
--Solved--
Dear all
At the moment I'm working on a rc-car, which has mounted a VLP16-HiRes on top of it. For processing the cloud and all other stuff a nVidia Jetson Xavier developer kit is mounted on the car. The OS is from nVidia, but is based on Ubuntu 18.04. The used ROS distro is melodic.
To achiv a non distorted cloud with the VLP16-HiRes, I changed the calibration file in the launch file
/opt/ros/melodic/share/velodyne_pointcloud/launch/VLP16_points.launch
to the correct file for the Hi-Res Puck (Line 7):
arg name="calibration" default="$(find velodyne_pointcloud)/params/VLP16_hires_db.yaml
Of course I make sure, that on the Web-Interface of the Sensor also the return mode is set to "Strongest" (as mentioned here for example).
As I understood it right, the ROS cannot make changes in the Velodyne settings (such as return mode, rpm, and so on).
So far everything is fine, as long as the car is not moving. As soon as I start moving I got all lines twice: Bellow you can find a little snipped of rviz (from the /velodyne_points topic):
Further I calculated for an object the estimated number of points. To be more precise I calculated the highest amount of points which I would the object expect to have. The cloud which represents the object, has more than the maximal possible amount of points. The one and only explanation I found, is that I'm running in the dual return mode.
As mentioned in several other posts and sources, I would expect the parameters of the ROS-File not to change anything on the sensor.
The comment in this post here says that probably the constant
VLP16_FIRINGS_PER_BLOCK = 2
could affect this. But I'm a bit aware of just changing the a constant, without any further understanding what it is used for.
I would appreciate it very much if someone can give me a hint how to solve the problem.
Best regards jerperfa
Update: I tested resetting (compiling and installing the library) with
VLP16_FIRINGS_PER_BLOCK = 1
Result: Size of cloud is reduced by halve, but I still have this second line. Can the movement of the car cause this line?
