Help required for PCL and opencv libraries with libfreenect

Hi,
I am using libfreenect drivers with C language on linux platform.My task is to find x,y,z coordinates of the markers placed on a human body joints which will be detected by kinect sensors i.e x,y coordinates from rgb camera of kinect and z from depth sensor of kinect.Can any one tell me how to use pcl library for finding out x,y,z coordinates of markers with opencv and Point cloud library.Waiting for your urgent help.
Thanks in advance.
Sana.