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Depth filter of a (Kinect) image

asked 2014-04-23 01:33:38 -0500

Poseidonius gravatar image


I run a Kinect sensor and evaluate depth and camera information to track positions of small robots. The idea is to use the pointcloud to identify all robots (2.5m < z < 3m). I used a pcl/passthrough filter for this purpose. Now I want to mask out all parts of the corresponding image which are not part of this cloud.

From my point of view I have to implement the following steps:

  1. Filter the point cloud (already available in pcl)
  2. Transfer the point cloud into an binary image (?)
  3. Mask the image (opencv?)

Other ideas? Thanks for your help.


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answered 2014-05-05 04:45:52 -0500

Poseidonius gravatar image

updated 2014-05-06 12:47:00 -0500


Ifound a solution for the problem and want to present them ... in order to motivate you for improvements:-) I used the

  • openni,
  • openni_launch,
  • depth_image_proc
  • pcl_ros
  • pcl_conversions

packages for ROS Hydro on Kubuntu 12.10. I used a ASUS Xtion for my setup.

1. Launch file

The solution combines 3 core elements:

  1. a nodelet, generating images and pointclouds based on the sensor
  2. a filter merging the 3D PointCloud and RGB Image information
  3. a filter that evaluates the depth values and adapts the RGB values
  4. a transormation that generates an image based on the PointCloud2.

The launch file illustrates the start up of these elements and follow at the end of the description part. I want to include some comments:

-> 1. The standard launch file $(find openni_launch)/launch/openni.launch has to be adapted related to the fact, that the following filter just accepts image and cloud data with the same frame id. I changed line 7 and 8 from the mentioned file

 <arg name="rgb_frame_id"   default="$(arg tf_prefix)/$(arg camera)_rgb_optical_frame" />
 <arg name="depth_frame_id" default="$(arg tf_prefix)/$(arg camera)_depth_optical_frame" />


 <arg name="rgb_frame_id"   default="$(arg tf_prefix)/$(arg camera)_optical_frame" />
 <arg name="depth_frame_id" default="$(arg tf_prefix)/$(arg camera)_optical_frame" />

in a new file myopenni.launch.

-> 2. The depth_image_proc package offers nodes for PointCloud2 processing. We use one of them for a fusion of point cloud data with corresponding RGB information. Take a view to the documentation on !

-> 3+4 The last two points are combined in the pointCloudToImage node. I wrote some lines of C++ to transform the ROS messages to PCL Pointcloud2 later to an pcl::PointCloud<pcl::pointcloudxyzrgb> object. It filters the RGB values according to the z coordinate. Afterwards the PointCloud2 is transformed to a ros image.

   #include <iostream>
   #include "ros/ros.h"
   #include <sensor_msgs/PointCloud2.h>
   #include <sensor_msgs/Image.h>
   #include <pcl/filters/passthrough.h>
   #include "pcl_conversions/pcl_conversions.h"

   #define Z_MIN 1.0
   #define Z_MAX 1.5

   ros::Publisher pub_cloud;
   ros::Publisher pub_image; 

   void cloudCallback(const sensor_msgs::PointCloud2 &ros_cloud)
     pcl::PCLPointCloud2 pcl_pc2;
     pcl_conversions::toPCL(ros_cloud, pcl_pc2); 
     pcl::PointCloud<pcl::PointXYZRGB>::Ptr pcl_cloud(new pcl::PointCloud<pcl::PointXYZRGB>);     
     pcl::fromPCLPointCloud2 (pcl_pc2, *pcl_cloud); 

     uint8_t r = 0;
     uint8_t g = 0;
     uint8_t b = 0;
     int32_t rgb = (r << 16) | (g << 8) | b; 

     for (size_t i = 0; i < pcl_cloud->points.size (); ++i)
       if ((pcl_cloud->points[i].z > Z_MAX) or (pcl_cloud->points[i].z < Z_MIN))
         pcl_cloud->points[i].rgb = rgb;
     pcl::toPCLPointCloud2 (*pcl_cloud, pcl_pc2);
     sensor_msgs::PointCloud2 ros_pc2;
     pcl_conversions::fromPCL(pcl_pc2, ros_pc2);

     pcl::PCLImage pcl_image;
     pcl::toPCLPointCloud2 (pcl_pc2, pcl_image);  
     sensor_msgs::Image ros_image; 
     pcl_conversions::fromPCL(pcl_image, ros_image);

   int main(int argc, char **argv)
     ros::init(argc, argv, "PointCloud2Filter");
     ros::NodeHandle n;
     ros::Subscriber sub = n.subscribe("input/", 1000, cloudCallback);
     pub_cloud = n.advertise<sensor_msgs::PointCloud2> ("output_cloud/", 30);
     pub_image = n.advertise<sensor_msgs::Image> ("output_image/", 30);
     return 0;

And the launch file ...

    <include file="$(find RoboMix)/launch/myopenni.launch" />

  <node pkg="nodelet" type="nodelet" name="pcl_manager" args="manager" output="screen ...
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Asked: 2014-04-23 01:33:38 -0500

Seen: 2,068 times

Last updated: May 06 '14