[ncl-talk] question about contour opacities

[Will Hobbs]

Thanks Rick, I hadn’t thought of changing the colormap itself. I’ll let you know it comes out.

will

From: Rick Brownrigg <brownrig at ucar.edu>
Date: Thursday, 25 March 2021 at 11:58 pm
To: Will Hobbs <will.hobbs at utas.edu.au>
Cc: "ncl-talk at mailman.ucar.edu" <ncl-talk at mailman.ucar.edu>
Subject: Re: [ncl-talk] question about contour opacities

Hi Will,

Offhand, I would think you could set up a custom colormap that consisted of RGBa tuples, which were all the same value for the 1st 3 components, and only the opacity (alpha) channel varied. Something like:

   myColors = new((/100,4/_, float)   ; colormap of 100 values
  do i=0,99
     mColors(i,:) = (/ 0., 0., 1., i / 100. /)   ;; transparent to solid blues
   end do

Then set either cnFillPalette or cnFillColors to "myColors"

   http://ncl.ucar.edu/Applications/rgbacolor.shtml<http://ncl.ucar.edu/Applications/rgbacolor.shtml>

Hope that helps...
Rick



On Thu, Mar 25, 2021 at 12:43 AM Will Hobbs via ncl-talk <ncl-talk at mailman.ucar.edu<mailto:ncl-talk at mailman.ucar.edu>> wrote:
Hi all

I suspect the answer is ‘no’, but is it possible to set multiple values for cnFillOpacity?

I’d like to plot an overlay that has a single fill color, but uses opacity as it’s ‘colourmap/contour level’.

I can see a way of doing this by looping through each contour level and setting explicit levels/opacities each time, but I wonder if there’s a more efficient way.

Will

Will Hobbs

Institute for Marine and Antarctic Studies (IMAS)
University of Tasmania
Private Bag 80, Hobart, 7001, TAS, AUSTRALIA
+61 3 6226 2970
imas.utas.edu.au<http://imas.utas.edu.au>
aappartnership.org.au<https://aappartnership.org.au>



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