Operator() on Vec3d?

1

I am reading the source code of opencv about the function initUndistortRectifyMapComputer.
I am confused about the below codes, what does vecTilt(2) represent , I think vec3d type has no () member functions.

Vec3d vecTilt = matTilt*cv::Vec3d(xd, yd, 1);
double invProj = vecTilt(2) ? 1./vecTilt(2) : 1;

2

https://docs.opencv.org/4.x/d6/dcf/classcv_1_1Vec.html#a4c3985698335fe7c60925a39697237ca

3

3-element vector
last element, (2), is the projective coordinate. that is why it is used for a divisor.

see also:

4

Yes, it is. Thank you very much.