function gauss2d, x, y, a
;;; How big are the abscissa arrays?
xnpix = n_elements(x)
ynpix = n_elements(y)
;;; Fan things out
xarr = rebin(x, xnpix, ynpix)
yarr = rebin(reform(y,1,ynpix), ynpix, xnpix)
;;; Rotate?
if n_elements(a) eq 7 then T = a[6] else T = 0.
;;; Advanced mathematical techniques
xp = (xarr-a[4]) * cos(T) - (yarr-a[5]) * sin(T)
yp = (xarr-a[4]) * sin(T) + (yarr-a[5]) * cos(T)
u = (xp / a[2])^2 + (yp / a[3])^2
g = a[0] + a[1] * exp(-U/2.)
return, g
end