=======Perception Tutorial=======

Tutorial describing first steps needed to start processing data from the Kinect, in the form of Point Clouds,  using tools included in ROS Fuerte.

==== 1. Prerequisite ====

Follow the steps described in [[software:ros:installation|Recommended procedure for installing ROS]] and [[software:ros:getting-started|Getting Started with ROS]]

If you are using a PrimeSense device (Xbox Kinect, Asus Xtion) check whether //ros-fuerte-openni-kinect// is installed. You can do this by running the following command in a terminal: 
  dpkg -l | grep  ros-fuerte-openni-kinect 
If not present install using:
  sudo apt-get install ros-fuerte-openni-kinect

Check out the code presented at seminar in your ros-workspace from:\\
[[https://github.com/ai-seminar/perception-tutorials.git]] \\
Prerecorded bag file can be found in ../tutorial_pkg/data/.

==== 2. Viewing and recording data from the Kinect ===

== Bag files and Rviz ==
For a PrimeSense device: connect it to your PC and run:
  roslaunch openni_launch openni.launch
Run rviz:
  rosrun rviz rviz
Add a new PointCloud2 display type to rviz, and choose // /camera/depth_registered_points // in the topics field. If rviz returns errors, change //Fixed Frame// in //Global Options// from //<Filxed Frame>// to one of the available ones in the dropdown list (e.g.  /camera_link)

Use //rosbag// to record data in a bag file, e.g.:
  rosbag record /camera/depth_registered/points /tf
Note: /tf is needed if you want to view the recorded data using rviz.
Play back a bag file using:
  rosbag play filename.bag --loop
More detail and a more elegant way of saving data from a Kinect to bag files can be found [[http://www.ros.org/wiki/openni_launch/Tutorials/BagRecordingPlayback|here]]

In order to save Point Clouds to *.pcd files run:
  rosrun pcl_ros pointcloud_to_pcd /input:=/camera/depth_registered/points
  
== Image_view ==
View rgb image:
  rosrun image_view image_view image:=/camera/rgb/image_color
View depth image:
  rosrun image_view image_view image:=/camera/depth/image
  
== From a ROS node ==

To see how you subscribe to a topic from a ros node take a look at //subscriber.cpp// from the source code.

==== 3.Processing Point Clouds ====

The following are presented in //tutorial.cpp//, for more detailed description check the links attached.
  * reading in a pcd file[[http://pointclouds.org/documentation/tutorials/reading_pcd.php#reading-pcd|link]]  
  * using PCLVisualizer[[http://pointclouds.org/documentation/tutorials/cloud_viewer.php#cloud-viewer|link]]
  * removing nans
  * calcultaing normals[[http://pointclouds.org/documentation/tutorials/normal_estimation.php#normal-estimation|link]]
  * filtering based on axes[[http://pointclouds.org/documentation/tutorials/passthrough.php#passthrough|link]]
  * downsampling the Point Cloud[[http://pointclouds.org/documentation/tutorials/voxel_grid.php#voxelgrid|link]]
  * RANSAC plane fitting, and extracting indices [[http://pointclouds.org/documentation/tutorials/planar_segmentation.php#planar-segmentation|link1]][[http://pointclouds.org/documentation/tutorials/extract_indices.php#extract-indices|link2]]

For further questions contact: //**balintbe** at **tzi** dot **de**//