Reading PointCloud2 in C++

asked 2011-03-02 15:17:18 -0600

Homer Manalo
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updated 2014-01-28 17:09:15 -0600

ngrennan
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How do you read a PointCloud2 in C++? I'm interested in getting the depth(z point). Maybe an equivalent of this: reading pointcloud2 in python.

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answered 2011-03-02 15:20:42 -0600

Eric Perko

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If you know what type of points you expect inside the PointCloud2, you can use the information from the pcl_ros wiki page for Subscribing to point clouds.

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Is the origin(0.0, 0.0) of points x and y at the center of frame? I'm seeing a negative y point here.

Homer Manalo ( 2011-03-02 18:40:01 -0600 )edit

That depends on whoever sends the pointcloud and what frame the data is in. For sensors the origin is usually (0,0,0). A negative y is also not unexpected. It could mean a point right or below the sensor (depending on the coordinate system)

dornhege ( 2011-03-02 21:58:07 -0600 )edit

I'm just using the pointcloud from stereo_image_proc. Where is the origin here? (top-left corner? top-right corner? center of the image?)

Homer Manalo ( 2011-03-03 00:09:48 -0600 )edit

What is the reported frame_id in the PointCloud2 you are reading?

Eric Perko ( 2011-03-03 04:27:19 -0600 )edit

The frame_id is [camera]. I actually have a warning message on the rviz console window saying [camera] is not a fully qualified frame_id (resolved locally to [/camera]). I have not setup any tf here.

Homer Manalo ( 2011-03-03 11:43:41 -0600 )edit

That warning isn't a big deal. The question I had was what sort of reference frame the PointCloud was using. According to the diagram and docs at http://www.ros.org/wiki/stereo_image_proc#stereo_image_proc.2BAC8-common.Nodes , /camera ought to be the frame of the left camera in the pair.

Eric Perko ( 2011-03-03 11:54:40 -0600 )edit

Note that that is an optical frame, with Z pointing along the camera's viewing axis, not a standard body frame. In that situation, the camera frame should be specified with an _optical suffix, as noted in REP 105: http://www.ros.org/reps/rep-0103.html#coordinate-frame-conventions .

Eric Perko ( 2011-03-03 11:55:48 -0600 )edit

For some reason, I did not notice that. Thanks.

Homer Manalo ( 2011-03-03 13:03:51 -0600 )edit

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answered 2018-09-07 01:33:34 -0600

Fetullah Atas

819 ●7 ●77 ●21 https://github.com/jediofgever

updated 2020-02-04 02:51:59 -0600

You seem already got an accepted answer but just for future reference,

You could use convertPointCloud2ToPointCloud from sensor_msgs.

Once you input Pointcloud2 and got output as Pointcloud , then you can iterate through your points as such;

#include <sensor_msgs/PointCloud.h>
#include <sensor_msgs/PointCloud2.h>
#include <sensor_msgs/point_cloud_conversion.h>

sensor_msgs::Pointcloud2 input_pointcloud;
sensor_msgs::Pointcloud out_pointcloud;
sensor_msgs::convertPointCloud2ToPointCloud(input_pointcloud, out_cloud);

for(int i = 0 ; i < out_cloud.points.size(); ++i){
    geometry_msgs::Point32 point;

    //Dooo something here
    point.z = out_cloud.points[i].z;
}

And get xyz coordinates of all points

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