Re: missing data

Hi Adam,

Continue with my last question.

Now I want to make a plot with one overlay on another. The data for the first plot have all values available, and second data have many missing values (as my earlier question). I used overplay command to try to put second on the first. Please see ncl script below. It didn't work since I got 2 plots instead one overlay plot. the error info is

fatal:NhlAddOverlay: plot class mapPlotClass cannot be overlay plot member

it looks like mapplot could be be overlay?

could you help me to fix the problem? thanks!

Xiaoyan

=========================================================
begin

   nlat = 46
   nlon = 72

   setfileoption("bin","ReadByteOrder","BigEndian")
   var = fbindirread("0.dat",0, (/46,72/), "float")
;=============================
;  create lat and long coordinate variables
;============================
   dlat  = 180./nlat
   dlon  = 360./nlon

   var!0          = "lat"
   var&lat        = ispan(-23,22,1)*dlat
   var&lat@units  = "degrees_north"

   var!1          = "lon"
   var&lon        = ispan(-36,35,1)*dlon
   var&lon@units  = "degrees_east"
;**************************************************
; create plot
;**************************************************
  wks = gsn_open_wks("ps","overlay")

  gsn_define_colormap(wks,"BlAqGrYeOrReVi200")  ; choose colormap

  res                  = True                      ; plot mods desired
  res@cnFillOn         = True                      ; turn on color
  res@cnLinesOn        = False                ; no contour lines

  res                       = True     ; plot mods desired

  res@tiMainString         = "Explict Contour Levels"
  res@cnFillOn              = True     ; turn on color fill
  res@cnLinesOn             = False    ; turn of contour lines
  res@gsnSpreadColors       = True     ; use full range of color map
  res@gsnSpreadColorStart = 20                  ; color to start
  res@gsnSpreadColorEnd   = 193                 ; color to end

  res@lbOrientation        = "vertical"  ; vertical label bar

  res@pmTickMarkDisplayMode = "Always"; use NCL default lat/lon labels
  res@gsnAddCyclic          = False    ; data already has cyclic point
                                       ; this must also be set for any zoom

  res@cnLevelSelectionMode = "ExplicitLevels"   ; set explicit contour levels
  res@cnLevels            = (/1e-4,5e-4,1e-3,5e-3,0.01,0.02,0.03,0.04,0.05/)
;===========================
; plot parameters
;===========================
 res@gsnDraw         = False                      ; do not draw
 res@gsnFrame        = False                      ; do not advance frame

 plot1  = gsn_csm_contour_map_ce(wks,var,res)     ; draw 1st contour
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

  var2 = fbindirread("1.dat",0, (/46,72/), "float")

  var2!0          = "lat"
  var2&lat        = ispan(-23,22,1)*dlat
  var2&lat@units  = "degrees_north"

  var2!1          = "lon"
  var2&lon        = ispan(-36,35,1)*dlon
  var2&lon@units  = "degrees_east"

  var2@_FillValue       = 0.0001                   ; sets _FillValue to 0.0001

  res2                            = True     ; plot mods desired
  res2@cnFillOn          = True                      ; turn on color
  res2@cnLinesOn        = False                ; no contour lines

  res2@tiMainString         = "Explict Contour Levels"
  res2@cnFillOn              = True     ; turn on color fill
  res2@cnLinesOn             = False    ; turn of contour lines
  res2@gsnSpreadColors       = True     ; use full range of color map
  res2@gsnSpreadColorStart = 20                  ; color to start
  res2@gsnSpreadColorEnd   = 193                 ; color to end

  res2@lbOrientation        = "vertical"  ; vertical label bar

  res2@pmTickMarkDisplayMode = "Always"; use NCL default lat/lon labels
  res2@gsnAddCyclic          = False    ; data already has cyclic point
                                       ; this must also be set for any zoom
  res2@cnLevelSelectionMode = "ExplicitLevels"   ; set explicit contour levels
  res2@cnLevels            = (/1e-4,5e-4,1e-3,5e-3,0.01,0.02,0.03,0.04,0.05/)

  res2@cnFillMode = "RasterFill"

 plot2  = gsn_csm_contour_map_ce(wks,var2,res2)     ; draw second plot

  overlay(plot1,plot2)                            ; now over lay plots

; the result of the overlay procedure is that the second argument is
; placed on top of the first. The first plot (now combined) is returned.

; these two step are required!
  draw(plot1)                     ; note we are drawing the first one!
  frame(wks)

end

On 10/05/11, "Xiaoyan Ma" <xiaoyan.ma@asrc.albany.edu> wrote:

Hi Adam,

Thanks for the quick reply. I did all except the last one. Now it works.

Thanks very much for the help.

Xiaoyan

On 10/05/11, Adam Phillips <asphilli@ucar.edu> wrote:

Hi Xiaoyan,
There might be a few problems here. Are you getting any error messages?
I would guess that you are... If you are the next time you send a
question to ncl-talk please include any error messages that you are
getting...

Does your var array have latitude/longitude coordinate variables
assigned to it? From the snippet of code you sent I don't see them..
You are reading in your data from a binary file, but when you do that
there will not be any information associated associated with your data
array that describes it. So, you need to assign that information to your
var array:

var!0 = "lat"
var&lat = ispan(-90,90,4)  ; I am guessing that your latitudes run from
                            ; -90:90 by 4.. You may need to change this.
var&lat@units = "degrees_north"

var!1 = "lon"
var&lon = ispan(0,355,5)   ; I am guessing that your longitudes run from
                            ; 0:355 by 6.. You may need to change this.
var&lon@units = "degrees_east"

By default, NCL will color fill areas denoted by the _FillValue
attribute as white. So you need to make sure that var@_FillValue is set
appropriately:

var@_FillValue =      ; set _FillValue, where data is missing, to the
                       ; appropriate value

Finally, and this might be most important, if your var array is mostly
composed of missing data, you are going to want to tell NCL to Raster
Fill, instead of Area Fill.. Going to Raster Fill will show each
individual grid box, while Area Fill may or may not.. So, add this:

res@cnFillMode = "RasterFill"

to your resource list.

If that advice doesn't solve your issue, please respond back to
ncl-talk.. Adam


On 10/05/2011 10:27 AM, Xiaoyan Ma wrote:
> Hi
>
> I want to create a contour plot from the observational data, i.e. for a
> 46*72 grid there are only ~ 100 points with observations, other points
> with missing data (I set a value as 0.0001). when I use ncl as below, I
> want to let those points with missing data as WHITE, but others as
> color. I do so in 2 ways:
>
> 1) set missing data as mask
> 2) set missing data as FillValue
>
> I do see there are values  of non-0.0001 by using print, but  the
> contour looks all white from 1) or 2). anybody tell me what is wrong?
>
> thanks a lot.
>
> Xiaoyan
>
> --------------------------------------------------------------------------
>    var = fbindirread("1.dat",0, (/46,72/), "float")
>
>   print(var)
> ;  var = mask(var,var.le.0.001,False)                 ; create
> artificial areas of missing data
>
>    var@_FillValue       = 0.0001                   ; sets _FillValue to
> 0.0001
>
>    res                  = True                      ; plot mods desired
>    res@cnFillOn         = True                      ; turn on color
>    res@cnLinesOn        = False                ; no contour lines
>
>    plot= gsn_csm_contour_map_ce(wks,var,res)
>
>
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--
______________________________________________________________
Adam Phillips                                asphilli@ucar.edu
NCAR/Climate and Global Dynamics Division       (303) 497-1726
P.O. Box 3000                        
Boulder, CO 80307-3000    http://www.cgd.ucar.edu/cas/asphilli
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