title: I writre freenect_camera_to_world myself, but
body: <p>I use opencv and openNi to calibrate the kinect and my HD camera,with the method in RGBDCaptureKinect,
  It use the freenect_camera_to_world to </p>
  
  <p>the origin code:</p>
  
  <pre><code>// camera -&gt; world coordinate helper function
  void freenect_camera_to_world(freenect_device* dev, int cx, int cy, int wz, double* wx, double* wy)
  {
      double ref_pix_size = dev-&gt;registration.zero_plane_info.reference_pixel_size;
      double ref_distance = dev-&gt;registration.zero_plane_info.reference_distance;
  
        // We multiply cx and cy by these factors because they come from a 640x480 image,
  
  // but the zero plane pixel size is for a 1280x1024 image.
  
  // However, the 640x480 image is produced by cropping the 1280x1024 image
  
  // to 1280x960 and then scaling by .5, so aspect ratio is maintained, and
  
  // we should simply multiply by two in each dimension.
  double factor = 2 * ref_pix_size * wz / ref_distance;
  *wx = (double)(cx - DEPTH_X_RES/2) * factor;
  *wy = (double)(cy - DEPTH_Y_RES/2) * factor;
  }
  </code></pre>
  
  <p>I write the freenect_camera_to_world function myself , but I have no idea is it right?</p>
  
  <pre><code>void freenect_camera_to_world(int cx,int cy,int wz, double *wx,double *wy)
  {
  double ref_pix_size = 0.1042; //how can I know these two value for my kienct?
  double ref_distance = 120.0; 
  
  double factor = 2*ref_pix_size*wz/ref_distance;
  *wx = (double)(cx - DEPTH_X_RES/2)*factor;
  *wy = (double)(cy - DEPTH_Y_RES/2)*factor;
  }
  </code></pre>
  
  <p>1、how can I know these two value for my kienct?ref_pix_size &amp; ref_distance</p>
  
  <p>2、and is it a standard for "the zero plane pixel size is for a 1280x1024 image."???</p>