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Pointcloud visualisation blinking when using Velodyne VLP16 dual return mode

asked 2015-07-01 05:07:29 -0600

Tohoku gravatar image

updated 2015-07-01 08:27:38 -0600

Hi everyone,

How to use ros package Velodyne for VLP16 dual return mode?

[Observed problem] 1. VLP16 hardware configuration was defined to dual return mode 2. I tried roslaunch velodyne_pointcloud VLP16_points.launch and display it on rviz, but the 3D point cloud was blinking and distorted.

[cause of the problem] The blinking was caused by dual return mode data structure . 1. Strongest return and Last return, the data structure: Every blocks have different horizontal angle. 2.However, Dual return data structure: Every 2 blocks are coupled with same horizontal angle.

Therefore it requires twice numbers of blocks to complete a 360 degrees of 3D point cloud in Dual return mode than the others. This have caused the blinking problem.

[how to solve it in ROS velodyne package] ???? need some help here

Thank you very much

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gvdhoorn gravatar imagegvdhoorn ( 2015-07-01 05:53:25 -0600 )edit
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Hi gvdhoom, the question "How to select dual return mode for velodyne VLP16?" can be solved by selecting dual mode in VLP16 hardware setting. However, this question is after the hardware setting, how to display point cloud in Velodyne ros package?.
=)

Tohoku gravatar imageTohoku ( 2015-07-01 07:06:21 -0600 )edit
1

Right. Then I suggest changing the title of your question to something like "Pointcloud visualisation blinking when using Velodyne VLP16 dual return mode". Because right now it's not clear from your question title what you're actually trying to do.

gvdhoorn gravatar imagegvdhoorn ( 2015-07-01 07:08:41 -0600 )edit

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answered 2015-07-01 08:56:27 -0600

joq gravatar image

The basic ROS sensor_msgs/LaserScan was supplemented with a similar sensor_msgs/MultiEchoLaserScan to handle multi-echo devices.

I know of no similar sensor_msgs/PointCloud2 enhancement, nor have I heard from any other developers with similar needs. I suppose there are various approaches one could take.

I recommend opening a discussion about it on the ros-sig-drivers mailing list. Perhaps we can develop a consensus on the best way to handle 3D multi-echo devices.

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answered 2018-07-15 19:19:06 -0600

Hi Tohoku, I was having the same problem, but I could find a solution.

First, you have to find the file "driver.cc". In there you will find some packet configuration for different types of velodyne lidars, and in some part you'll find the next:

else if (config_.model == "VLP16") { packet_rate = 754; // 754 Packets/Second for Last or Strongest mode 1508 for dual (VLP-16 User Manual) model_full_name = "VLP-16"; }

So, you have to change the packet rate to 1508, which is the packet rate for dual returns. This will solve the problem.

Now, there is another issue, the classification of the last return and the strongest/2nd strongest return, because now they are indistinguishably. If someone have an idea of how to do the classification, I'll be very grateful for the help!

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Asked: 2015-07-01 05:07:29 -0600

Seen: 1,328 times

Last updated: Jul 01 '15