pointcloud2 and path planning

edit

currently running ubuntu 16.04, ros kinetic, using gazebo 7 simulation with a sawyer (intera 5.2), running kinect camera.

I want to take a point from a point cloud (type PointCloud2) taken from the kinect frame. point would be of type PointXYZRGBNormal. I want to take the point, use a transformation to get the point in the world frame, then input that into a script i wrote that performs inverse kinematics to determine a pose for sawyer.

My script takes a point input in the form of a position (xyz) and a quaternion (xyzw). I also want to be able to subscribe to the pointcloud rostopic and index through the points to select a single point and its relevant data.

can anyone suggest how to take the PointXYZRGBNormal and convert the information to a position and quaternion in the world frame?

Please let me know if more information is required.

Any help/suggestions would be much appreciated.

~ Luke

EDIT:

I want to be able to transform the kinect point cloud from the camera frame to the world frame. At this stage, i can't even extract a point from the point cloud to transform. after transforming the point cloud, i want to be able to select a point, then perform inverse kinematics to move to that point (i'm already able to perform IK to determine a pose).

I've tried to use transformPointCloud in python. See code below:

    def transform_cloud(self):
    tfBuffer = tf2_ros.Buffer()
    listener = tf2_ros.TransformListener(tfBuffer)
    transformer = tf.TransformerROS(True,rospy.Duration(1.0))
    pcl_sub = rospy.Subscriber("/downsampled_cloud", PointCloud2)
    pub_trans = rospy.Publisher('pub_trans', TransformStamped, queue_size = 10)
    trans_cloud = rospy.Publisher('trans_cloud', PointCloud2, queue_size = 10)

    rate = rospy.Rate(1)
    while not rospy.is_shutdown():
        try:
            trans = tfBuffer.lookup_transform('base', 'depth_link', rospy.Time.now(), rospy.Duration(1.0))
            print type(trans)
            pub_trans.publish(trans)
            cloud_trans = transformer.transformPointCloud('base', pcl_sub)
            trans_cloud.publish(cloud_trans)
        except (tf2_ros.LookupException, tf2_ros.ConnectivityException, tf2_ros.ExtrapolationException):
            print("lookup failed")
            pass
        rate.sleep()

Doing this yields the following in terminal:

File "/opt/ros/kinetic/lib/python2.7/dist-packages/tf/listener.py", line 325, in transformPointCloud
    r.header.stamp = point_cloud.header.stamp
AttributeError: 'Subscriber' object has no attribute 'header'

It is worth noting that the PointCloud i'm trying to transform (/downsampled_cloud) does have a header. So i'm not sure why it's saying the subscriber doesn't have a header attribute.

Any help is much appreciated.