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Errors in Velodyne driver

asked 2016-06-09 05:18:37 -0500

Kailegh gravatar image

updated 2016-06-16 02:25:09 -0500

Hi, I am working with a VLP-16. I am using the ros driver to get de pointcloud. However I think there are some mistakes in the driver. If you change the angle in the web, for example, using only 90 degrees, the total amount of points per scan changes, and in the driver is kept constant. When you change the rpm of the velodyne to 1200 the rate should be 20 Hz, however the driver still thinks te speed is 600rpm. I have made a couple of changes and I have been able to solve the problem with the angle by ading a new parameter, with the speed I have done something similar but it still have some issues.

Have anybody else seen those mistakes?

The best way to solve them would be retrieving the information directly from the velodyne, but that is not so easy and it would requiere a big effort from me (I am still new to this).

EDIT: I mean changing the angle and the speed here:

If the angle is different from 359 it does not work well. It accumulates measurments until reach the equivalent number of points to 359 Hz, and therefore the laser rate decreases. For example, if yo select 90 degrees, it will work at Hz. How do I open a git issue? I have been able to solve both problems using arguments, however I think that someone should make the driver to read the parameters from within the Velodyne

Thanks a lot!

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Your questions are unclear. What is the "angle in the web"? Did you set the "rpm" parameter correctly?

joq gravatar image joq  ( 2016-06-09 11:02:57 -0500 )edit

If you believe you have found a bug in the driver, please open a github issue, explaining how to reproduce the error.

joq gravatar image joq  ( 2016-06-09 11:03:34 -0500 )edit

sorry, I did not see that the rpm parameter is in other file launch, I included one myself. However the problem with the selected angle is real.

Kailegh gravatar image Kailegh  ( 2016-06-13 07:21:50 -0500 )edit

I still have no idea which angle you are talking about. Note that, as a ROS standard, angles are always represented in radians.

joq gravatar image joq  ( 2016-06-15 11:23:20 -0500 )edit

when you put the velodyne IP in the web browser you can configure it (the image I showed). There is a parameter called FOV, you can change the start and the end, by the defaul is set to 0-359, so the VLP-16 gives a whole turn. If you change it, eg 0-90 the driver does not works properly.

Kailegh gravatar image Kailegh  ( 2016-06-16 02:28:46 -0500 )edit

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answered 2016-06-15 11:25:21 -0500

joq gravatar image

updated 2016-06-16 09:13:23 -0500

Changes you make in the device configuration menus are not known to the ROS driver.

EDIT: as you discovered, the driver has no knowledge of changes you made in the device configuration page.

For example: if you reconfigure the rotational speed, you also need to set the driver's rpm parameter. But, the driver has no parameters for you to notify it that you have changed the device's field of view.

The point cloud generator does provide an alternative via its view_direction and view_width parameters. Those options have some advantages and disadvantages when compared with changing the device configuration:

  • A disadvantage is that the device still needs to send the entire 360 degree field of view, which uses more ethernet bandwidth.
  • An advantage is that the view direction and width can be steered dynamically while the system is running via the various ROS dynamic reconfiguration interfaces.
  • Most of the system-level overhead is converting the raw data to 3D points. That can be reduced by using those parameters intelligently.
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ok, thanks a lot then, I will try my alternative and your proposal and see what works better. thanks again

Kailegh gravatar image Kailegh  ( 2016-06-17 05:47:58 -0500 )edit

Please report back the results of your experiments.

joq gravatar image joq  ( 2016-06-17 10:35:41 -0500 )edit

excuse me, I know it may be a silly question, but I do not see the view_direction and view_width parameters in the launche files. I see them in the, and I think they will work fine, but I try passing them as arguments and it does not work for me. Are you sure everything is ok?

Kailegh gravatar image Kailegh  ( 2016-06-23 06:39:36 -0500 )edit

I mean, where do I have to pass the desired view_direction and view_width? Thanks a lot

Kailegh gravatar image Kailegh  ( 2016-06-23 06:56:02 -0500 )edit

It's not an argument to the launch scripts. You can make a copy of the cloud_nodelet.launch, and add the appropriate <param ... /> lines. For a quick experiment: run the rqt GUI and select Plugins>Configuration>Dynamic Reconfigure.

joq gravatar image joq  ( 2016-06-27 11:17:36 -0500 )edit

I would accept a pull request adding those parameters as arguments to the various launch scripts.

joq gravatar image joq  ( 2016-06-27 11:18:27 -0500 )edit

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Asked: 2016-06-09 05:18:37 -0500

Seen: 1,102 times

Last updated: Jun 16 '16