PointSpreadFunction2DGaussian:

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   Compute the point spread function for a 2D gaussian.
   This is the shape of a star that is effectively a point light source.
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   Form:
       PointSpreadFunction2DGaussian;
   i = PointSpreadFunction2DGaussian( p, p0, sigma, i0 )
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   ------
   Inputs
   ------
   p             (2,:)  [x;y] positions
   p0            (2,1)  Center
   sigma         (1,1)  Sigma
   i0            (1,1)  Intensity peak

   -------
   Outputs
   -------
   i             (y,x)  2D Gaussian

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	Reference: Bruce R. Hancock, Robert C. Stirbl,Thomas J. Cunningham,
	           Be@brata Pain,Chris J. Wrigley, Peter G . Ringold Jet"CMOS Active
              Pixel Sensor Specific Performance Effects on Star Tracker 
              Imager Position Accuracy", Propulsion Laboratory, California
              Institute of Technology, Pasadena, CA 91109
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Children:

Common: Graphics/Mesh2