Why OpenCV has only 6 extrinsic parameters in calibration function?

Question

I use the Opencv sample code to do the camera calibration. As far as I know, the extrinsic parameter have 12 elements but in the OpenCV the sum of rotation vector and translation vector is 6.

Why OpenCV has only 6 parameters ?

http://docs.opencv.org/2.4/_downloads/camera_calibration.cpp

in line 525, it's say that "a set of 6-tuples" cvWriteComment( *fs, "a set of 6-tuples (rotation vector + translation vector) for each view", 0 ); — Shih-Wei Ho, Mar 20 '16 at 07:38

score 2 · Answer 1 · answered Mar 26 '17 at 03:36

calibratecamera method In calibrateCamera method output rvecs and tvecs, 3D vector for rotation(since any rotation matrix has just 3 degrees of freedom) and translation. They use Rodrigues method to convert 3x4 matrix R to 3D vector r. Thus, only 6 extrinsic parameters.

Why OpenCV has only 6 extrinsic parameters in calibration function?

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