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MIP Multi-Camera Calibration

Corner Detection / Selection

  • After pressing ok, the configuration GUI will disappear and the calibration program is started with the main window and an image list.
  • You now have to select all inner corners of the checkerboard in the images.

Image

  • The software tries to automatically detect the corners of the checkerboard. If the detection is successful the checkerboard will be marked in the image as displayed in the image above. If it could not be detected you have to click the outer four corners using the mouse. Left click sets a corner, right click lets you start over. Always select the corners in the same way. Corner 1 has to be the same physical corner in all images and the direction of selection has to be the same!
  • If you only click the outer four corners the other inner corners are interpolated. For cameras with big lens distortions it is advisable to select all corners. To do so check the "Select All Corners" checkbox. Then you have to select the corners rowwise, starting always at the left from top to bottom.
  • Later Versions of the software feature an auto-detection button in the menubar. Pressing it the software will detect corners in all images and mark the valid and invalid ones. It will stop if corners could not be detected in an image.
  • Later Versions also have an auto-invalidate feature which automatically invalidates images in which the corners could not be detected. Menuitem Corners->Auto Invalidate Images
  • It is also possible to scale the images for convenience and corner detection. Use the "Rescale" control in the menu bar. Sometimes the automatic corner detection works better if the images are enlarged or shrinked.
  • To navigate through the images, use "Previous" and "Next" or click on the image name in the image list.
  • If you want to skip an image, press "Invalidate"
  • After selecting all corners in all images save your corners by selecting the Menuitem Corners->SaveCorners.

Approximation / Calibration

  • After selection of all corners in all images press "Approximate". This will approximate the camera position relative to the checkerboard for each image and it will approximate the intrinsic camera parameters of all cameras.
  • Deprecated in versions > 0.8.5: After that press "Mean". This will make the mean of all relative orientations and positions of all cameras in the camera rig. If only one camera is used nothing will happen.

Image

  • After that press "Calibrate". This starts the real calibration algorithm, minimizing the reprojection error in all images for all valid pixels.


Image

  • You can follow that process looking at the reprojections by selecting from the menu: Reprojection->ShowReprojection.

Obtaining the Results

  • During and at the end of the calibration process you can save the calibration results by selecting Calibration->SaveRig from the menu.
  • The result will be a file in which all camera parameters are saved. This file is in the format of the BIAS::ProjectionParameters. See our software and documentation site for details. BIAS Software
  • The position and rotation of the first camera is set to zero. The positions and rotations of all other cameras are given relative to this first camera.


Verifying the Results

  • When the calibration is done you can save the images with the projections by selecting Calibration->Save Images with Poses from the Menu. This saves all images with the calibration parameters in the image headers in files "oldname_res.xxx".
  • From version 0.8.8 the installation package comes with the BIASEpipolarGeometryViewer software. This software can be used to check the quality of the calibration. The Software takes two images and two projections (Camera Parameters) as input. If the Camera Parameters are included in the images (as it is in this case) giving two images is sufficient. It displays the images side-by-side when a point in the left image is clicked with the mouse it draws the epipolar line in the right image. If the calibration was successful the epipolar line in the right image should go through the point corresponding to the clicked point in the left image.


Good Luck!

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Created by ischiller. Last Modification: Thursday 16 of July, 2015 11:46:56 CEST by sandro.