Inverse perspective map

Hi there,

I recently bumped into this repo, nice work! I was wondering why there is no nodelet to calculate the birds eye view image based on a homography matrix using:

https://docs.opencv.org/2.4/modules/imgproc/doc/geometric_transformations.html (cv.WarpPerspective)

Is there any reason that this nodelet not exists? If not, I'm happy to send a PR.