PRO geoster,lat0,long0,alt,maxza,latarr,longarr,degrees=degrees,zoom=zoom
; Make arrays of (x,y) values for a stereographic projection centered
; at latitude lat0 and longitude long0.  To be used for mapping PoCa
; images to geographic coordinates.

IF NOT KEYWORD_SET(degrees) THEN BEGIN
    phi_p=!RADEG*lat0
    lambda_p=!RADEG*long0
    ENDIF ELSE BEGIN
    phi_p=lat0
    lambda_p=long0
    ENDELSE

IF KEYWORD_SET(zoom) THEN ht=alt ELSE ht=300.
maxrad=za2dist(maxza,ht,degrees=degrees,radius=relc(phi_p))

x=REBIN((FINDGEN(192)-95.5)*maxrad/96,192,192)
y=TRANSPOSE(x)

re=relc(phi_p)+alt

alpha=ATAN(x,y)
h=!PI/2.-2.*ATAN(SQRT(x*x+y*y),2.*re)

sinphi=SIN(phi_p*!DTOR)*SIN(h)+COS(phi_p*!DTOR)*COS(h)*COS(alpha)
latarr=ASIN(sinphi)
sindlam=SIN(alpha)*COS(h)/COS(latarr)
longarr=lambda_p*!DTOR+ASIN(sindlam)

IF KEYWORD_SET(degrees) THEN BEGIN
    latarr=!RADEG*latarr
    longarr=!RADEG*longarr
    ENDIF

RETURN
END