Cloud-based Object Recognition Engine (CORE)

CORE is a framework for performing object recognition on 3D point cloud data [1]. It includes machine learning classifiers, a Robot Operating System (ROS) [2] module, and wraps existing data filters, feature descriptors, and segmentation techniques found in the Point Cloud Library (PCL) [3]. The goal of CORE is to leverage cloud computing facilities for the purpose of storing data, training classifiers, and performing object recognition tasks offloaded by network connected robots.

Building CORE on Ubuntu 14.04

First, install the prerequisite software:

$ sudo apt-get install libconfig++-dev

Next, install PCL:

$ sudo add-apt-repository ppa:v-launchpad-jochen-sprickerhof-de/pcl  
$ sudo apt-get update  
$ sudo apt-get install libpcl-all  

Then, build CORE:

$ cd core  
$ mkdir build && cd build  
$ cmake ..  
$ make  
$ sudo make install  
$ echo '/usr/local/lib' | sudo tee /etc/ld.so.conf.d/usr-local-lib.conf > /dev/null  
$ sudo ldconfig  

Install ROS Indigo [2] and build the ROS module:

$ cd core/ros  
$ catkin_make

Usage

Remote server example

Server setup

We use CloudLab [4] as our remote computing facility in this example. We've created a profile (disk image) named 'ubuntu-14_04-ros-indigo-full' that captures the entire cloud environment. This profile is shared within CloudLab under the project 'core-robotics'. It consists of one x86 node running Ubuntu 14.04 with ROS Indigo installed.

After starting an experiment with the above profile, clone and build CORE:

$ git clone https://[email protected]/wjbeksi/core  
$ cd core  
$ mkdir build && cd build  
$ cmake ..  
$ make  
$ sudo make install  
$ echo '/usr/local/lib' | sudo tee /etc/ld.so.conf.d/usr-local-lib.conf > /dev/null  
$ sudo ldconfig  

Next, build the ROS module:

$ cd core/ros  
$ source /opt/ros/indigo/setup.bash  
$ catkin_make  

Then, launch the rosbridge server node:

$ cd core/ros   
$ source devel/setup.bash   
$ roslaunch rosbridge_server rosbridge_websocket.launch  

Finally, in another terminal launch the CORE server nodes:

$ cd core/ros   
$ source devel/setup.bash   
$ roslaunch core_server core_server.launch  

Client setup

Follow the instructions above for building CORE on the client (robot). We'll assume that you have an RGB-D sensor connected, such as the Asus Xtion, with the necessary driver modules installed (OpenNI and PrimeSense). Proceed by launching the ROS OpenNI2 driver:

$ roslaunch openni2_launch openni2.launch depth_registration:=true 

Then, launch the CORE client nodes:

$ cd core/ros   
$ source devel/setup.bash   
$ roslaunch core_client core_client.launch server_ip_addr:=xxx.xxx.xxx.xx:9090

where 'xxx.xxx.xxx.xx' is the IP address of the CloudLab server found by using the command 'if_config'.

Point clouds captured by the client will be preprocessed (filtered, culled, compressed, etc.) and sent to the remote server for classification.

Standalone classification example

In this example, we show how to use CORE for object classification using covariance descriptors and a support vector machine (SVM).

Computing the covariance descriptor for a set of PCD files

First, copy over the CORE configuration file, 'core.cfg', from the 'configuration' subdirectory. To adjust filter, segmentation, descriptor, and learning parameters, edit this file as necessary. Then, create a file named 'pcd_categories' that contains a list of absolute paths to PCD files, one category per line. The covariance files are written out for each category under the directory 'covariance_dir':

$ compute_covariance core.cfg pcd_categories covariance_dir  

Learning an SVM model based on covariance descriptors

The learning parameter, gamma, is set in the configuration file 'core.cfg'. The model is constructed using the file 'cov_categories' which contains the absolute paths, one category per line, to the covariance files created in the previous step:

$ svm_learn_model core.cfg cov_categories  

SVM classification based on covariance descriptors

Now we can predict the classification labels of objects in a point cloud given the configuration file, the trained SVM model, and a test input PCD file:

$ svm_predict_class core.cfg model.txt pc_1.pcd 

References

[1] W.J. Beksi, J. Spruth and N. Papanikolopoulos, "CORE: A Cloud-based Object Recognition Engine for Robotics", IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), pp. 4512-4517, 2015.
[2] Robot Operating System: http://www.ros.org
[3] Point Cloud Library: http://www.pointclouds.org
[4] CloudLab: https://www.cloudlab.us