Check3D - camera calibration tool for 3D analysis


Quick start guide


1. Individual camera calibration

The first step in any analysis is to perform a camera calibration.  Select New in the Calibration Library.

Enter the relevant board details for your specific analysis. The values for the sample images are given in the above screenshot.

Click Proceed to continue.



A camera calibration window will appear.  The calibration images are shown in the left hand side of the window.  Click 'Calibrate' and wait for the operation to complete (this may take over a minute if you have got a large number of images).  The calibration window is shown above.

  1. If the checkerboard is not completely visible in the image then click 'Exclude' on that image.

  2. The number alongside each calibration image is the RMS pixel error for the reconstruction of the intersection points on the checkerboard.  The overall projection error is shown in the 'Parameters' table.  If any image has a pixel error which is considerably larger (as a guide, double the overall projection error), you should consider excluding that image.

  3. The image in the bottom-right of the screen should show a circle (geometrical centre of the image) and a crosshair (calculated principal point of the camera). For most modern cameras/lenses the two points should coincide very closely. If they do not, consider selecting Fix principal point and running the calibration again.

  4. If lens distortions are obvious, or suspected, it is worth running a calibration with Calculate radial distortions selected.  If the overall projection error is not reduced significantly then unselect this option.  Furthermore, move the mouse over the image in the bottom-right of the screen and this will display the calculated distortion (in pixels) at any point in the image.  If the maximum distortion is small (as a guide, less than 2% of the image dimension) then it is advisable to unselect Calculate radial distortions

  5. In general, the option Calculate tangential distortions should not be used.  This option is generally only useful if the longitudinal axis of the lens is badly aligned to the camera sensor.

  6. The graph in the centre of the window shows the pixel error of each intersection point on the checkerboard. 

  7. To view a larger version of any image, click on it and the image will be shown in the top-right of the window.

When you are happy with the calibration, click Next to calibrate the right camera. Repeat the steps above for that camera.

For a description of the camera parameters have a look at the Jean-Yves Bouguet's camera calibration site.


2. Stereo camera calibration

On the stereo calibration window, leave the default settings and click Calibrate.  Any excluding images from the individual calibration stage will also be excluding in this stage (along with their associated image in the other camera view). 

The pairs of images in both cameras must be synchronised.  If they are not, the solver will either fail(crash) or give the wrong stereo model.

  1. The reprojection error is the RMS of the total reprojection error for all the points (see OpenCV for full description).  The algorithm minimises this value to find the optimal solution.
  2. If the Fix intrinsic parameters is selected, Check3D will use the same camera model as obtained in the individual calibration stage.  This is the most stable method.  You may wish to deselect this option.  This allows the stereo calibration algorithm to recompute the intrinsic camera parameters to minimise the stereo reprojection error.


3. Specify origin system

This stage can be skipped if you do not want to specify a local origin system for the digitised data.

This completes the specification of the origin system, and any coordinate obtained using this calibration will be referenced to this origin.  The stereo calibration file will be saved in the '..\MyDocuments\Check3D\Calibration' folder, and listed in the Calibration Library in Check3D.  The uniqueID is used to identify the calibration and is the same as the filename.

Calibrations can be exported/imported so that they can be used on other computers.