title: convert a 3d point from camera space to object space, in c++ with opencv
body: <p>In computer vision, when I need to convert a cv::mat from object(world) space coordinates to camera space, or a camera-centric coordinate, i use the following
  code: ( where <code>rvec</code> and <code>tvec</code> are the rotation and translation vectors of the camera)</p>
  
  <pre><code>cv::Mat R; //holds rotation matrix
  cv::Rodrigues(rvec, R); // converts a rotation vector to a 3x3 matrix
  R = R.t();  // rotation of inverse
  tvec2 = -R * tvec; // translation of inverse
  </code></pre>
  
  <p>giving me <code>tvec2</code> as the camera space coordinate. </p>
  
  <p>My current problem is the opposite. I have an array of 3d points in camera space, and i need to convert them to world space. What does the inverse of the above function look like?</p>
  
  <p>Thank you.</p>