请教，ncl图空白部分如何去除？

wongsubao

刚学ncl，依葫芦画瓢写了个程序画图，由于是时序图，想用长方形的，看起来美观点，可是四周空白老去不掉，也使用过将背景设为透明，但整张图片的框架还是没变。请教各位帮忙看下，如何解决，在此多谢！
源程序
load"$NCARG_ROOT/lib/ncarg/nclscripts/contrib/time_axis_labels.ncl"
load"$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
load"$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
load"$NCARG_ROOT/lib/ncarg/nclscripts/contrib/cd_string.ncl"
begin
vild=(/"AQI","VIS","PM25","PM10","O3","NO2","SO2","CO"/)
filename="2016071820.txt"
data =asciiread(filename,-1,"string")
yy=tointeger(str_get_cols(data,0,3))
nm=tointeger(str_get_cols(data,4,5))
dd=tointeger(str_get_cols(data,6,7))
tt=tointeger(str_get_cols(data,8,9))
nt=dimsizes(yy)
times= new(nt,"float")
do i = 0,nt-1
times(i)=i
end do
units="hours since"+yy(0)+"-"+nm(0)+"-"+dd(0)+""+tt(0)+":00:00"
xbrange =tointeger(cd_inv_calendar((/yy(0),yy(nt-1)/), (/nm(0),nm(nt-1)/),(/dd(0),dd(nt-1)/), (/tt(0), tt(nt-1)/), (/0, 0/), (/0, 0/), units, 0))
xbvalues = ispan(xbrange(0), xbrange(1),12)
xbvalues@units = units
xblabels = cd_string(xbvalues,"%d.%H")
npts=dimsizes(xbvalues)
y=stringtofloat(str_get_cols(data,16,22))
rws ="png"
wks=gsn_open_wks(rws,"test")
res = True
res@gsnMaximize = True
;  res@vpWidthF =0.9
;  res@vpHeightF = 0.5
;  res@vpXF =0.1
;  res@vpYF=0.9
res@gsnBoxMargin = 0.0
res@tmXTOn = False
res@tmYLFormat = "f"
restick = True
  res@tmXBMode="Explicit"
   res@trXMinF=xbrange(0)
  res@trXMaxF = xbrange(1)
  res@tmXBTickSpacingF = 6
  res@tmXBValues = xbvalues
  res@tmXBLabels = xblabels
  res@pmTickMarkDisplayMode = "Always"
  res@tiMainFontHeightF = 0.025
  res@tiYAxisFontHeightF = 0.02
    res@tiMainString = "test test"
  plot=gsn_csm_xy(wks,times,y,res)
end

出图1，左右两边到边上，上下有较多空白

设置

rws@wkHeight = 600

rws@wkWidth = 900

后出图2，四周都多出空白

另外设置rws ="oldpdf"
res@vpWidthF =0.9
res@vpHeightF = 0.6
后出图3，四周边倒是比较好，可为什么图会横过来？？？

xiaogao

正好需要，楼主强大！