tutorial_1_grasps_camera.md

Tutorial 1 - Detect Grasps With an RGBD Camera

In this tutorial, we will detect grasp poses using an RGBD camera such as the Microsoft Kinect or Asus Xtion Pro.

1. Setup

Connect an RGBD camera to your robot/computer.

All of the following commands need to be run in separate terminals/tabs. First, start the driver for your camera.

roslaunch openni2_launch openni2.launch

Next, start rviz.

rosrun rviz rviz

In rviz, load the config file gpd/tutorials/openni2.rviz.

2. Detect Grasps

Launch the ROS node that detects grasps.

roslaunch gpd tutorial1.launch

This will produce grasps on the ROS topic /detect_grasps/grasps. An example is shown below.

3. Use the Grasps in Python

To use the grasps, start up your favorite Python editor and enter the following code.

import rospy
from gpd.msg import GraspConfigList

# global variable to store grasps
grasps = []


# Callback function to receive grasps.
def callback(msg):
    global grasps
    grasps = msg.grasps


# ==================== MAIN ====================
# Create a ROS node.
rospy.init_node('get_grasps')

# Subscribe to the ROS topic that contains the grasps.
sub = rospy.Subscriber('/detect_grasps/clustered_grasps', GraspConfigList, callback)

# Wait for grasps to arrive.
rate = rospy.Rate(1)

while not rospy.is_shutdown():
    print '.'
    if len(grasps) > 0:
        rospy.loginfo('Received %d grasps.', len(grasps))
        break
    rate.sleep()

This code creates a ROS node that waits for grasps. Once grasps arrive, the node prints the number of grasps receveived and exits. You can start from this code to use our grasp detection algorithm on your robot!

2. Troubleshoot

No Grasps Found

If the algorithm does not find grasps, it's usually because the workspace (workspace) is too large or that the number of samples (num_samples) drawn from the point cloud is too small. You can change the corresponding parameters in the launch file (launch/openni2_15_channels.launch).

3. Switching to PCL visualization

If you prefer PCL's cloud visualization, open the file launch/openni2_15_channels.launch, set the parameter rviz_topic to an empty string, "", and set any of the parameters starting with plot_ to True. Those parameters allow to plot different steps in the algorithm. For example, the following setting plots the detected grasps using pcl.

<param name="plot_normals" value="false" />
<param name="plot_samples" value="false" />    
<param name="plot_candidates" value="false" />
<param name="plot_filtered_grasps" value="false" />
<param name="plot_valid_grasps" value="false" />
<param name="plot_clusters" value="false" />
<param name="plot_selected_grasps" value="false" />
<param name="rviz_topic" value="grasps_rviz" />