camCoor = np.array([0.,0.,0.,1.])

      camCoor[2] = cam.near
      deltaY = (cam.top - cam.bottom)/cam.imageHeight
      deltaX = (cam.right - cam.left)/cam.imageWidth
      camCoor[0] = deltaX * col + cam.left
      camCoor[1] = deltaY * row + cam.bottom