; map_axis
;
; Draws axes on cylindrical equidistant map images created by ce_image.pro
; and image.pro

; Variables used...
; nxt --- Number of major tick mark intervals along x
; nyt --- Number of major tick mark intervals along y
; xtv --- Number of major tick marks along x 
; ytv --- Number of major tick marks along y
; minlon ---
; maxlon ---
; minlat ---
; maxlat ---
; xtl --- (xticklength)
; ytl --- (yticklength)
; xtn --- (xtickname)
; ytn --- (ytickname)
; xlab -- (xlabel)
; ylab --- (ylabel)
; mxt --- (xminor) minor tick intervals per major tick interval along x
; myt --- (yminor) minor tick intervals per major tick interval along y
; xtn --- labels for xaxis for both minor ticks and major ticks 
; ytn --- labels for yaxis
; left_off --- take out the left axis
; bottom_off ---  take out the bottom axis
; label --- to label E/W and N/S
; right -- add and label axis on right side of plot
; top --- add and label axis on top of the plot
; nprec - The number of decimal points precision for the labels

pro map_axis, nxt, nyt, minlon, maxlon, minlat, maxlat, xtl, ytl, xtn, ytn, $
              xtv, ytv, xlab, ylab, mxt, myt, left_off, bottom_off, label, $
              right, top, nprec=nprec

;
; Draw the axis
;
if (n_elements(nprec) EQ 0) then nprec=0
if (n_elements(xtv) EQ 0) then begin
  xtickset=1
  xtv=fltarr(nxt+1)
endif
if (n_elements(ytv) EQ 0) then begin
  ytickset=1
  ytv=fltarr(nyt+1)
endif
if (keyword_set(top)) then begin
  if (nxt GT 0) then begin
    if (keyword_set(xtickset)) then begin
      for i=0,nxt do xtv(i) = minlon + i*(maxlon-minlon)/nxt
    endif
    if n_elements(xtn) EQ 0 then begin
      if (keyword_set(label)) then begin
        xtn=gen_labels(xtv[0],xtv[nxt],nxt,'W','E',nprec=nprec)
      endif else begin
        xtn=gen_labels(xtv[0],xtv[nxt],nxt,'','',nprec=nprec)
      endelse
    endif

    axis,xaxis=1,xticklen=xtl,xtitle=xlab,xrange=[minlon,maxlon], $
      xstyle=9,xticks=nxt,xminor=mxt,xtickv=xtv,xtickname=xtn

  endif else begin
    axis,xaxis=1,xticklen=xtl,xtitle=xlab,xrange=[minlon,maxlon],xstyle=9
  endelse
endif
if (NOT keyword_set(bottom_off)) then begin
  if (nxt GT 0) then begin
    if (keyword_set(xtickset)) then begin
      for i=0,nxt do xtv(i) = minlon + i*(maxlon-minlon)/nxt
    endif
    if n_elements(xtn) EQ 0 then begin
      if (keyword_set(label)) then begin
        xtn=gen_labels(xtv[0],xtv[nxt],nxt,'W','E',nprec=nprec)
      endif else begin
        xtn=gen_labels(xtv[0],xtv[nxt],nxt,'','',nprec=nprec)
      endelse
    endif

    axis,xaxis=0,xticklen=xtl,xtitle=xlab,xrange=[minlon,maxlon], $
      xstyle=9,xticks=nxt,xminor=mxt,xtickv=xtv,xtickname=xtn

  endif else begin
    axis,xaxis=0,xticklen=xtl,xtitle=xlab,xrange=[minlon,maxlon],xstyle=9
  endelse
endif

if (NOT keyword_set(left_off)) then begin
  if (nyt GT 0) then begin
    if (keyword_set(ytickset)) then begin
      for i=0,nyt do ytv(i) = minlat + i*(maxlat-minlat)/nyt
    endif
    if n_elements(ytn) EQ 0 then begin
      if (keyword_set(label)) then begin
        ytn=gen_labels(ytv[0],ytv[nyt],nyt,'S','N',nprec=nprec)
      endif else begin
        ytn=gen_labels(ytv[0],ytv[nyt],nyt,'','',nprec=nprec)
      endelse
    endif

    axis,yaxis=0,yticklen=ytl,ytitle=ylab,yrange=[minlat,maxlat], $
      ystyle=9,yticks=nyt,yminor=myt,ytickv=ytv,ytickname=ytn

  endif else begin
    axis,yaxis=0,yticklen=ytl,ytitle=ylab,yrange=[minlat,maxlat],ystyle=9
  endelse
endif

if (keyword_set(right)) then begin
  if (nyt GT 0) then begin
    if (keyword_set(ytickset)) then begin
      for i=0,nyt do ytv(i) = minlat + i*(maxlat-minlat)/nyt
    endif
    if n_elements(ytn) EQ 0 then begin
      if (keyword_set(label)) then begin
        ytn=gen_labels(ytv[0],ytv[nyt],nyt,'S','N',nprec=nprec)
      endif else begin
        ytn=gen_labels(ytv[0],ytv[nyt],nyt,'','',nprec=nprec)
      endelse
    endif

    axis,yaxis=1,yticklen=ytl,ytitle=ylab,ytickname=ytn,yrange=[minlat,maxlat],$
         ystyle=9,yticks=nyt,yminor=myt,ytickv=ytv

  endif else begin
    axis,yaxis=1,yticklen=ytl,ytitle=ylab,yrange=[minlat,maxlat],ystyle=9
  endelse
endif

end