title: Aligning Matlab CVST's 3D stereo co-ordinate system along local vertical and local horizontal
body: <p>Using stereo vision <a href="http://www.mathworks.com/products/computer-vision/" rel="nofollow">Computer Vision System Toolbox by Mathworks</a>, I am able to reconstruct the object under inspection.</p>
  
  <p>After calibration, I know the co-ordinate system which stereo setup uses is mentioned <a href="http://in.mathworks.com/help/vision/gs/coordinate-systems.html?refresh=true" rel="nofollow">here</a> (it is wrt optical centre of Camera 1).</p>
  
  <p>I have noticed that the same co-ordinate system may not be followed in real world 3D. For example, the local vertical (of a place, which can be found using a spirit level) need not align with the vertical axis (y-axis) of my stereo setup's co-ordinate system.</p>
  
  <p>Suppose I move my object only along the local vertical, without any change in its x position (i.e. local horizontal of that place), according to the stereo co-ordinate system used by the cameras, my object would have moved along y axis (obviously), and also along the x-axis of camera (which is not right, since according to the real world, my object hasn't been moved along local horizontal at all!).</p>
  
  <p>How can I tackle this issue? I am aligning the stereo setup according to the local vertical and local horizontal (using a spirit level), as well as my object. Still, when I move it along local vertical only, there is a few mm change in x-coordinate reading as well. Any inputs regarding this would be appreciated.</p>