Check2D - camera calibration tool for 2D kinematic analysis

Overview

Check2D is a software package that has been developed by the Centre for Sports Engineering Research at Sheffield Hallam University.  It uses the planar camera calibration technique from the OpenCV function library.

 The software allows the user to:

  1. Calibrate the intrinsic parameters of the camera
  2. Calibrate the extrinsic parameters of the camera
  3. Digitise test footage using different marker size/shape and calculate the 2D position of the marker

 

An overview of each stage is given below:

Create a checkerboard calibration object

The calibration object needs to satisfy the following criteria:

  1. Be flat
  2. Have equal number of squares in the horizontal and vertical directions
  3. Have either a large white or black border around the checkerboard pattern
 

 

Calibrate the intrinsic parameters of the camera

  1. Move checkerboard around the field-of-view making sure:
    • the entire sensor area is covered
    • the checkerboard is in focus
    • the checkerboard is rotated sufficiently between images
  2. Create New Calibration in Check2D software using the collected images.
  3. Check2D software detects the intersections between the black and white squares which are used by the algorithm to create the intrinsic camera model.
  4. Invalid images are excluded from the calibration.

Calibrate the extrinsic parameters of the camera

  1. Points at known locations on the control volume plane are used to determine the extrinsic parameters of the camera.
  2. In the tennis court image above, a selection of court markings could be used.
  3. A minimum of four points is required

Digitise markers in the trial footage

  1. Corresponding markers in both camera views are digitised and then reconstructed into 2D coordinates within Check2D.
  2. This data can be exported to the clipboard or to a .csv file.