I'm studying essential matrix and fundamental matrix and notice that the formula on OpenCV's site does not confirm to what I learnt elsewhere.
It says '[p2;1] (K^T) E(K) [p1;1] = 0' but wouldn't it be '[p2;1] (K^-T) E (K^-1) [p1;1] = 0' since 'F = (K^-T) E (K^-1)'. And for essential matrix, 'p2^T E p1 = 0' just takes the camera coordinate so '[p2;1] (K^-T) E (K^-1) [p1;1] = 0' is correct from my opinion since it transfers the image coordinate to the camera coordinate by multiplying the inverse K matrix, which is for the intrinsic parameters of the camera.
The doc containing the formula is here http://docs.opencv.org/3.0-beta/modules/calib3d/doc/camera_calibration_and_3d_reconstruction.html#findessentialmat