camera_calibration circle grid pattern

Hello, i have a question regarding the camera_calibration package. Basically i need some help how to use it with a circle grid. The tutorial is only about chessboard grids which are working fine, but i want to use i highly accurate target, which is basically a circle grid. I am not able to set up the arguments (pattern, size, square) correctly. The cameracalibrator is displaying the image of the camera, but he is not trying to fit the circles. Short: How can ich use grid patterns like this one http://wiki.ros.org/visp_camera_calibration/Tutorials/CalibrationExternalCamera?action=AttachFile&do=view&target=grid2d.pdf together with the camera_calibration package? What is in this case the pattern, square and size? Thanks for your help guys.