In my case, i use four sets of points to do the Bird's Eye Projection.But i forgot to do the camera calibration first!
So i want to know is the result is same doing Camera calibration before Bird's Eye Projection and after Bird's Eye Projection in OpenCV?
Can you give me some advice?Thank you very much.
Can you specify what calibration do you refer to? There are generally 2 kinds of camera parameters you can estimate during calibration - intrinsic and extrinsic.
Intrinsic parameters can be for simplicity assumed 'fixed' for particular camera, which includes lens and sensor. Those parameters typically include focal length, sensor's dimensions, and distortion coefficients.
Extrinsic parameters are 'dynamic', and typically refer to camera position and orientation.
Now, if you represent those as some abstract transformations - they don't commute, which means you can't change their order. So, if you want to apply homography to an image - you have to undistort it first, because generally homography maps plane to another plane, and after distortion your planes will be messed up.
But on the other hand, once you apply one transform, you can estimate how much of other transform you have 'left to do'. This is OK for linear stuff, but turns ugly if you warp distorted image using homography and THEN try to undistort it.
Tl,Dr - perform intrinsic calibration and undistortion first, since it is easier and they are fixed for camera, then apply your transformations.
