FUNCTION gaussian_2d_arr, hsize, fwhm_a, fwhm_b, x0, y0, theta, hires

; Description: This function creates a two-dimensional output pixel array representing an (elliptical) 
;              Gaussian profile with a major axis of FWHM "fwhm_a" pixels, a minor axis of FWHM "fwhm_b" 
;              pixels, an angle "theta" in degrees as measured anti-clockwise from the x-axis to the
;              major axis, and its centre at pixel coordinates "(hsize + 0.5 + x0, hsize + 0.5 + y0)".
;              The output pixel array is returned as a square array of side "(2*hsize) + 1" pixels. The 
;              pixel values are calculated from a pixel grid that samples the Gaussian profile at "hires" 
;              times the resolution of the output pixel array, which gives the user the option of 
;              accurately calculating the integrals over the discrete pixels. Finally, the output pixel 
;              array is normalised to a peak value of 1.
;
; Input Parameters:
;
;   hsize - INTEGER/LONG - The output array is returned as a square array of side "(2*hsize) + 1" pixels.
;                          If this parameter is negative, then it will be reset to "0".
;   fwhm_a - FLOAT/DOUBLE - The Gaussian major axis FWHM (pix). This parameter must be positive, or the 
;                           function will fail and return a value of "0.0".
;   fwhm_b - FLOAT/DOUBLE - The Gaussian minor axis FWHM (pix). This parameter must be positive, or the 
;                           function will fail and return a value of "0.0".
;   x0 - FLOAT/DOUBLE - The offset along the x-axis of the Gaussian centre from the centre of the output 
;                       pixel array (pix).
;   y0 - FLOAT/DOUBLE - The offset along the y-axis of the Gaussian centre from the centre of the output 
;                       pixel array (pix).
;   theta - FLOAT/DOUBLE - The angle as measured anti-clockwise from the x-axis to the Gaussian major 
;                          axis (deg).
;   hires - INTEGER/LONG - The oversampling factor to be used to calculate the output pixel array. This
;                          parameter has a minimum allowed value of "1", corresponding to no oversampling,
;                          and a maximum allowed value of "10", to protect against unnecessary oversampling
;                          using too much memory allocation.
;
; Return Value:
;
;   The function returns a square pixel array of DOUBLE precision values and of side "(2*hsize) + 1" 
;   pixels representing the required Gaussian profile. If the function fails, then it returns a value   
;   of "0.0".                
;
; Author: Dan Bramich (dmb@ing.iac.es)
;
; History:
;
;   16/07/2008 - Module created (dmb)

;Force the half size of the output pixel vector to be at least zero

;Check the parameters "fwhm_a", "fwhm_b", "x0", "y0" and "theta"

;Force the oversampling factor to be at least 1, and limit its maximum value to 10

;Convert the Gaussian FWHMs to Gaussian sigmas

;Generate the coordinate arrays for the oversampled pixel array

;Calculate the values of the Gaussian profile for the oversampled pixel array

;Bin the oversampled pixel array by the oversampling factor "hires"

;Normalise the output pixel array to a peak value of 1

;Return the output pixel array representing the Gaussian profile