Suppose that we have an image on the plane, which borders are parallel to coordinate axis. This procedure does the mapping from plane coordinates to pixels of image.

Mapping from plane coordinates to image pixels

#! /usr/bin/python

# We lay sides of image parallel to axi of planes
# Bigger side of image maps to bigger side of rect
# On images we always have X ~ Width, Y ~ Height (it is true for OpenCV)
def PlaneToImage(Point, LTCorner, RBCorner, resW, resH):
    assert(not resW==resH)
    if (resW > resH):
        if (abs(LTCorner[0]-RBCorner[0]) > abs(LTCorner[1]-RBCorner[1])):
            OnImgX, OnImgY = 0, 1
        else:
            OnImgX, OnImgY = 1, 0
    else:
        if (abs(LTCorner[0]-RBCorner[0]) > abs(LTCorner[1]-RBCorner[1])):
            OnImgX, OnImgY = 1, 0
        else:
            OnImgX, OnImgY = 0, 1

    OWidth, OHeight = float(RBCorner[OnImgX]-LTCorner[OnImgX]), float(RBCorner[OnImgY]- LTCorner[OnImgY])
    NImgX, NImgY = float(Point[OnImgX]-LTCorner[OnImgX])/OWidth, float(Point[OnImgY]-LTCorner[OnImgY])/OHeight
    return [int(resW*NImgX), int(resH*NImgY)]