/* File     : jitter.c
 *
 * Contents :
 *	Compute_jitter : Convolve PSF with a jitter function
 *
 * Author   : John Krist (STScI)
 * Date     : January 1992
 */

#include <stdio.h>
#include <math.h>
#include "tinytim.h"

/*---------------------------------------------------------------------
*  Compute_jitter :
*	Convolve the PSF with a jitter function.
*
*  Inputs :
*	Crit_psf   :  Complex array containing critically sampled PSF.
*	dim        :  dimension of Crit_psf (dim x dim).
*	wavelength :  wavelength of PSF in microns.
*	jitter     :  RMS jitter in milliarceconds.
*			
*----------------------------------------------------------------------*/
void Compute_jitter( complex **crit_psf, int dim, float wavelength, float jitter )
{
	float	c, v, radius, dist, dist_sqr[4096], y_sqr;
	int	x, y;


	/* Create a lookup table of distances.  The table is shifted *
	 * to account for the shifting of the OTF.  This essentially *
	 * creates a jitter function shifted to (0,0).		     */

	radius = dim / 2;

	for ( x = 0; x < dim/2; ++x )
	{
		dist = x / radius;
		dist_sqr[x] = dist * dist;
	}

	for ( x = dim / 2; x < dim; ++x )
	{
		dist = (dim - x) / radius;
		dist_sqr[x] = dist * dist;
	}

	/* Multiply the OTF (FFT of PSF) by the jitter function */

	c = M_PI * jitter * 4.848e-9 * DIAM_HST_MICRONS / wavelength;

	for ( y = 0; y < dim; ++y )
	{
		y_sqr = dist_sqr[y];

		for ( x = 0; x < dim; ++x )
		{
			v = sqrt(dist_sqr[x] + y_sqr) * c;
			v = exp( -2.0 * v * v );
			crit_psf[y][x].r *= v;
			crit_psf[y][x].i *= 0.0;
		}
	}

} /* Compute_jitter */