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   Computes the camera angle from aperture diameter, imaging element
   diameter and focal length.
   Type CameraAngleFromGeometry for a demo
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   Form:
   theta = CameraAngleFromGeometry( d, rho, f )
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   Inputs
   ------
   d              (1,1)       Aperture diameter
   rho            (1,1)       Imaging element diameter
   f              (1,1)       Focal length

   -------
   Outputs
   -------
   theta          (1,1)       Field of view

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