Re: Associating specific colors with specific contour levels?

From: Arindam Chakraborty <achakrab_at_nyahnyahspammersnyahnyah>
Date: Thu, 31 Jul 2008 15:18:31 -0400

hi Gary,
    you can do this in NCL. You can define your own colormap using gsn_define_colormap() function:

 cmap = (/(/1,1,1/) \
       ,  (/0,0,0/) \
       ,  (/0.8,0.2,0.2/) \ ; 2 (r,g,b)
       ,  (/0.6,0.2,0.4/) \ ; 3
       ,  (/0.4,0.4,0.1/) \ ; 4
       ,  (/0.4,0.6,0.2/) \ ; 5
       ,  (/0.2,0.8,0.2/) \ ; 6
       ,  (/0.2,0.9,0.5/) \ ; 7
       ,  (/0.0,1.0,0.0/) \ ; 8
       /)
gsn_define_colormap(wks,cmap)

See NCL documention for further details on this. Also, you can assign a specific color for a specific contour level using resources cnLevels and cnFillColors. See the attached file for a simple example.
For the irregular contouring levels in your example, use ispan() thrice to make three separate arrays, and then join them to make  a single array and use that in cnLevels.

hope this helps,

arindam


Gary Strand wrote:

I'm attempting to replicate a Ferret code that I have in NCL, and one of the things Ferret allows you to do is associate specific colors with specific contour levels. One does this by giving the contour level and color triplet in the colormap file used, e.g.:

RGB_Mapping By_Value

! Val    R    G    B

-6000.   0.   0.  20. ! blue-black

-4000.  10.  18.  90.

-2000.  20.  35. 100. ! blue

-300.   40.  70. 100. 

-100.   50. 100. 100.

 -50.   40.  80.  70.

  -0.1  90. 100. 100. ! light green-blue

   0.    0.  40.  00. ! dark green

 100.    0.  70.  30. ! light green

 300.   90. 100.   0. ! light yellow

1200.   60.  30.   0. ! rust

4000.   90.  90. 100. ! ice blue

5000.  100. 100. 100. ! white

Is there a way to do something like this in NCL?

Also, can I specify contour levels in "chunks" without having to specify all of them explicitly? Ferret allows you to this via the "LEV" command:

shade/lev=(-10250,-250,250)(-250,250,25)(250,8250,250) topo

That is, from -10250 to -250, use 250 increments, from -250 to 250, increment by 25, and then from 250 to 8250, go back to 250.

Thanks!

 

Gary Strand

strandwg@ucar.edu

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-- 
----------------------------
 ARINDAM CHAKRABORTY
 Department of Meteorology
 Florida State University
 Tallahassee, FL-32306, USA
 Tel: 850-644-3524 (O)
      850-524-0717 (C)
 Fax: 850-644-9642
____________________________

load "$NCARG_ROOT/lib/ncarg/nclex/gsun/gsn_code.ncl"
load "$NCARG_ROOT/lib/ncarg/nclex/gsun/gsn_csm.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"

begin

 nx=10
 ny=10

 var = new((/ny,nx/),"float")

; var = random_normal(0,1,(/ny,nx/))

 do j = 0,ny-1
  do i = 0,nx-1
   var(j,i) = i+j
  end do
 end do

 wks = gsn_open_wks("X11","fill")

 cmap = (/(/1,1,1/) \
       , (/0,0,0/) \
       , (/0.8,0.2,0.2/) \ ; 2
       , (/0.6,0.2,0.4/) \ ; 3
       , (/0.4,0.4,0.1/) \ ; 4
       , (/0.4,0.6,0.2/) \ ; 5
       , (/0.2,0.8,0.2/) \ ; 6
       , (/0.2,0.9,0.5/) \ ; 7
       , (/0.0,1.0,0.0/) \ ; 8
       /)
; gsn_define_colormap(wks,"WhBlGrYeRe")
 gsn_define_colormap(wks,cmap)

 res = True
 res_at_cnFillOn = True
 res_at_cnLinesOn = False
; res_at_cnLevels = fspan(-5.0,5.0,21)
; res_at_gsnSpreadColors = True
 res_at_cnLevelSelectionMode = "ExplicitLevels"
 res_at_cnLevels = (/1,2,4,8,16,32/)
 res_at_cnFillColors = (/2,3,4,5,6,7,8/)

 plt = gsn_csm_contour(wks,var,res)
end

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Received on Thu Jul 31 2008 - 13:18:31 MDT