PointCloud subscriber/publisher types

asked 2011-03-23 03:37:45 -0500

Ivan Dryanovski

4954 ●52 ●70 ●86 http://robotics.ccny.cuny.edu/

updated 2011-03-24 21:04:13 -0500

tfoote

58457 ●128 ●550 ●526 http://www.ros.org/

Hi,

When working with PointClouds, I usually subscribe to a sensor_msgs::PointCloud2 topic, and convert to a pcl::PointCloud inside my code. Then, once I'm done mainpulating the cloud, I convert it back to a sensor_msgs::PointCloud2 to publish it, using these functions:

pcl::fromROSMsg
pcl::toROSMsg

My first question is: what is the cost of using these functions? I am assuming there's a memcpy involved, which (when dealing with kinect data) is probably not negligible.

Second: is there a way to avoid this, by directly subscribing/publishing pcl::PointCloud types? I believe that there is a publisher/subscriber for pcl types, but I'm not sure whether it actually saves time, or does the same conversion/memcpy behind the scenes.

Thanks, Ivan

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answered 2011-03-24 21:04:02 -0500

tfoote

58457 ●128 ●550 ●526 http://www.ros.org/

The conversion to and from PCL datatypes is quite computationally expensive. I have observed something like 100ms for a conversion of a Kinect frame on a 1Ghz Atom core.

To avoid this you can use direct publication of pcl datatypes and nodelets. A very simple example of a nodelet which does this is in the pointcloud_to_laserscan package is cloud_throttle.cpp

When publishing over the network the Kinect data was unusable.

Using nodelets I was able to take processing of the Kinect from 10Hz and 150% cpu to 30Hz and 87% cpu on an Atom by publishing using the exact same data type. Here's a launch file which brings up the kinect and processes the data inside the same process using nodelets.

Comments

what about the second part of the question? when publishing / subscribing directly with pcl PointCloud, does it first convert to sensors_msgs::PointCloud2 then serialize, then deserialize and convert to PCL? Or does it serialize deserialize directly from / to PCL? I am not using nodelets.

brice rebsamen ( 2013-12-19 14:06:42 -0500 )edit

If ti does require conversion it will directly convert to the wire format to or from the pcl datatype.

tfoote ( 2013-12-19 14:11:36 -0500 )edit

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