; main 
; fast_modpat

    NX=64                    ; size of modul patrn map (map pixels)
    F1_length=2048.          ; size of F1d table  (table pixels)
    pitch=30                 ; pitch in arc sec
    xoffset=64               ; offset from spin axis in asec
    yoffset=64
    aspp=2                   ; asec per map pixel
    delta=0                  ; collimator phase in asec
    s2p=0.5                  ; slit/pitch ratio

s=findgen(F1_length)*2*!pi/pitch
                     ; slit/pitch ratio

; CREATE A SYNTHETIC 1-D MODULATION PATTERN:
d=[s2p^2,0,0,0]
n= [1,2,3]           ; use 1st 3 harmonics for triangle waveform
d(n)=(1-cos(2*!pi*n*s2p))/(!pi^2*n^2)
f1d=d(0)+d(1)*cos(s)+d(2)*cos(2*s)+d(3)*cos(3*s)

; INTRODUCE PSEUDO RANDOM JITTER AND SPIN-AXIS MOTION:
theta=findgen(360)*!dtor
dx=2.*(randomu(seed,360)-0.5)+20.*cos(theta)  ; random jitter+ellipt. motion
dy=2.*(randomu(seed,360)-0.5)+25.*sin(theta)  ; random jitter+ellipt. motion

t=systime(1)
xpixel=0 & ypixel=0  ; FORCE MODPAT1D TO COMPUTE XPIXEL, YPIXEL ARRAYS
for i=0,359 do begin
 theta=i*!dtor
 z=modpat1d(NX,F1D,theta,aspp,xoffset,yoffset,dx(i),dy(i),xpixel,ypixel)
; tvscl,reform(z,NX,NX),0
endfor
time=systime(1)-t
print,'elapsed time=',time,' time per modpat=',time/float(i)

end