;
; PURPOSE: Grid spacing
; WRITTEN: May 1993 	Xuepu Zhao
; Modified: May 2006	Xuepu Zhao
;
PRO zgrid06,iph,jth,phd,thd,lad,cth,sth,cmp,csc,scs,RUP=rup

    if N_params() LT 1 then begin
       print,'PRO zgrid06,iph,jth,phd,thd,lad,cth,sth,cmp,scs,/rup'
       return
    endif
; calculate cth,sth,thd,phd
    thd = fltarr(jth)
    lad = thd
    sth = thd
    cth = thd
    phd = fltarr(iph)
    dcth=2.0/jth
    for j=0,jth-1 do begin
        cth(j)=(j+0.5)*dcth-1.0          ; from south to north
        thr=acos(cth(j))
        sth(j) = SIN(thr)
        thd(j) = thr/!dtor
        lad(j) = 90-thd(j)
    endfor
    dph=360./iph
    for i=0,iph-1 do phd(i) = i*dph+dph  ; from left to right
; calculate csc,scs
    if n_elements(cmp) eq 1 then begin
       csc=fltarr(jth)
       cpc=fltarr(iph)
       scs=cpc
       for j=0,jth-1 do csc(j)=1/sth(j)
       for i=0,iph-1 do begin
           dphr=(phd(i)-cmp)*!dtor
           cpc(i)=cos(dphr)
           scs(i)=1/cpc(i)
       endfor
     endif
     if keyword_set(rup) then begin
        lphd=phd & lthd=thd & llad=lad & lcth=cth & lsth=sth & lscs=scs
        for j=0, jth-1 do begin
            thd(j)=lthd(jth-j)
            lad(j)=llad(jth-1)
            cth(j)=lcth(jth-j)
            sth(j)=lsth(jth-1)
        endfor
        for i=0,iph-1 do begin
            phd(i)=lphd(iph-i)
            scs(i)=lscs(iph-i)
        endfor
     endif

END