I have a small confusion regarding the use of the solvePnP function in OpenCV.
I have the matrix for the intrinsic parameters of the camera and I have identified some keypoints in image and I am trying to estimate the extrinsic parameters for the calibration.
The documentation for solvePnP says:
cv2.solvePnP(objectPoints, imagePoints, cameraMatrix,
distCoeffs[, rvec[, tvec[, useExtrinsicGuess[, flags]]]]) → retval, rvec, tvec
I am guesisng my imagePoints parameters are the keypoints I have detected. and these arte specified in pixels as (x1, y1), (x2, y2), (x3, y3).
I am totally confused about the objectPoints. So, the documentation says:
objectPoints – Array of object points in the object coordinate space,
3xN/Nx3 1-channel or 1xN/Nx1 3-channel, where N is the number of points.
vector<Point3f> can be also passed here.
How can I generate these object points from my image points? What does it mean when they say the object coordinate space in here?
The cv2.solvePnP() method is generally used in pose estimation, or in other words, it can be used to estimate the orientation of a 3D object in a 2D image. So for this you need to tag some key-points in the 3D model of the object(objectPoints) and also detect those key-points in the 2D image(imagePoints).
You can consult this answer, to get the application of this technique for face pose estimation.