[ncl-talk] White for zero in a map

[Jiang, Lifen]

Hi Mary,

Thank you very much for writing the script for me! But it showed below error when I ran it. I have attached the script and my data file again. It will be helpful if you or anybody else can help tell the problem.

fatal:Undefined identifier: (span_color_indexes) is undefined, can't continue
fatal:Execute: Error occurred at or near line 23 in file diff_test.ncl

Thanks again,

Lifen
______________________________
From: Mary Haley [haley at ucar.edu]
Sent: Tuesday, March 03, 2015 3:29 PM
To: Jiang, Lifen
Cc: ncl-talk at ucar.edu
Subject: Re: [ncl-talk] White for zero in a map

There are many ways you can do this.

I've attached a script that does this by using the cnFillColors resource to specify a list of color indexes into the "rainbow" color map, but then I changed the color index that represents level 0.0 to be 0 (the background color, and therefore white).

--Mary


On Sun, Mar 1, 2015 at 3:01 PM, Jiang, Lifen <lfjiang at ou.edu<mailto:lfjiang at ou.edu>> wrote:
Hello,

I was trying to create a map of the attached variable. The min and and max are -14 and 18, respectively.

I would like to set white for zero, but could not work out how to make it. Script is at the end of this email.

Could anybody help with my issue?

I appreciate your time and help!

Thanks,

Lifen


;************************************************
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/csm/contributed.ncl"

begin

  in = addfile("Diff.nc","r")
  t  = in->Diff
  t at _FillValue  = -999
  t at missing_value = t at _FillValue

  printVarSummary(t)

  wks = gsn_open_wks("png" ,"Plot_Diff")                ;
  gsn_define_colormap(wks,"rainbow")        ; choose colormap

  res                       = True     ; plot mods desired

  res at cnFillOn              = True     ; turn on color fill
  res at cnLinesOn             = False    ; turn off contour lines
  res at cnLevelSpacingF       = 3      ; contour spacing

;---This resource not needed in NCL V6.1.0
  res at gsnSpreadColors       = True     ; use full range of color map

  res at lbLabelStride         = 1

  res at pmTickMarkDisplayMode = "Always"; use NCL default lat/lon labels

  res at gsnAddCyclic          = False    ; data already has cyclic point
                                  ; this must also be set for any zoom

; note that the gsn_csm_*map_ce templates automatically set
; res at mpLimitMode="LatLon" for you. If you are plotting a different projection,
; you may have to set this resource.

  res at mpMinLatF            = -90      ; range to zoom in on
  res at mpMaxLatF            =  90
  res at mpMinLonF            = -180
  res at mpMaxLonF            = 180

  res at cnLevelSelectionMode = "ManualLevels"
  res at cnMinLevelValF       = -15
  res at cnMaxLevelValF       = 20

  plot = gsn_csm_contour_map_ce(wks,t({-90:90},{-180:180}), res)


end

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