Module to connect to a kinect through ROS + OpenNI and access the skeleton postures.

kinect.py

# encoding: utf-8


"""Module to connect to a kinect through ROS + OpenNI and access
the skeleton postures.
"""


import roslib
roslib.load_manifest('ros_skeleton_recorder')
import rospy
import tf


BASE_FRAME = '/openni_depth_frame'
FRAMES = [
        'head',
        'neck',
        'torso',
        'left_shoulder',
        'left_elbow',
        'left_hand',
        'left_hip',
        'left_knee',
        'left_foot',
        'right_shoulder',
        'right_elbow',
        'right_hand',
        'right_hip',
        'right_knee',
        'right_foot',
        ]
LAST = rospy.Duration()


class Kinect:

    def __init__(self, name='kinect_listener', user=1):
        rospy.init_node(name, anonymous=True)
        self.listener = tf.TransformListener()
        self.user = user

    
    def get_posture(self):
        """Returns a list of frames constituted by a translation matrix
        and a rotation matrix.

        Raises IndexError when a frame can't be found (which happens if
        the requested user is not calibrated).
        """
        try:
            frames = []
            for frame in FRAMES:
                trans, rot = self.listener.lookupTransform(BASE_FRAME,
                        "/%s_%d" % (frame, self.user), LAST)
                frames.append((trans, rot))
            return frames
        except (tf.LookupException,
                tf.ConnectivityException,
                tf.ExtrapolationException):
            raise IndexError

It happens because the TF frame may not be available all the time. So its better to wait until the next TF frame is available.
Add the following line :

self.listener.waitForTransform(BASE_FRAME, "/%s_%d" % (frame, self.user), rospy.Time(), rospy.Duration(4.0)

before:
(trans, rot) = self.listener.lookupTransform(BASE_FRAME,"/%s_%d" % (frame, self.user), LAST)