[ncl-talk] printing the names of colors used in legendbar of contour plot

[Tabish Ansari]

Hi Mary,

Thanks for providing this script. I've been able to plot my required wrf
data alongside observational station data with the same colorscale.
However, my WRF data is on a Lambert Conformal projection but this scripts
plots it on a cylindrical equidistant projection. I would like to plot it
nicely on its native projection i.e., lambert conformal.

I would also like to switch on the map boundaries (national and state, grid
lines, geophysical etc.) on both the plots. Could you please help me do
this?

Thanks a lot!

Tabish

Tabish U Ansari
PhD student, Lancaster Environment Center
Lancaster Univeristy
Bailrigg, Lancaster,
LA1 4YW, United Kingdom

On 28 August 2016 at 20:11, Mary Haley <haley at ucar.edu> wrote:

> ​Hi Tabish,
>
> Here's a some extra information on colors in NCL:
>
> -------------------------------------------------------------------------
> When you use a predefined colormap, like "rainbow" or "amwg", it is not
> defined by named colors, by rather by RGBA quadruplets.
>
> RGBA arrays are N x 4 floating point arrays of values that go from 0 to 1,
>  where the 'RGB' represents fractions of red, green, and blue, and the 'A'
> represents the 'alpha' value which designates the opacity of the color.
>
> For example:
>
> The color (/1.0,0.,0.,1./)  represents red, because you have full red
> (1.0), no green (0.0), no blue (0.0), and full opacity (1.0).
>
> The color (/0.0,1.0,0.0,1./) represents green, with full opacity.
>
> The color (/0.0,0.0,1.0,0.5/) represents blue, with half opacity.
>
> The color (/1.0,1.0,0.0,0.25/) represents yellow, with a quarter opacity.
>
> etc.
>
> In NCL, when you specify a color resource like:
>
>   res at gsMarkerColor = "red"
>
> you can use named colors, but you can also use direct RGBA values:
>
>   res at gsMarkerColor = (/1.,0.,0.,1./)   ; fully opaque red marker
>
> The nice thing about using RGBA values is it allows you to control the
> opacity, for example:
>
>   res at gsMarkerColor = (/1.,0.,0.,0.25/)   ; mostly transparent red marker
> ---------------------------------------------------------------------
>
> Anyway, you can mimic the colors that NCL uses in your WRF plot, by using
> span_color_rgba.  You need to give this function the same levels that you
> are using for the contour plot, and it will return the same colors being
> used by the contour plot. Note, you could accomplish the same thing by
> calling "getvalues" on the smoothed contour plot to retrieve the levels and
> the colors.
>
> See the attached script, which creates a filled contour plot of SLP, and
> then randomly grabs points from SLP to mimic an observational data set, but
> draws these values using filled square markers.
>
> You can get the dataset from:
>
> http://www.ncl.ucar.edu/Applications/Data/cdf/wrfout_
> d01_2003-07-15_00:00:00
>
> --Mary
>
>
>
> On Sat, Aug 27, 2016 at 9:38 PM, Tabish Ansari <tabishumaransari at gmail.com
> > wrote:
>
>> Hi
>>
>> I'm trying to compare wrf model output (contour plot) with some station
>> data (scattered observations). I am trying to color the markers of the
>> station data based on their values and create a similar legend bar as the
>> wrf-contour. However, this is not very straightforward as I'm using
>> predefined colormap for wrf-contour but have to explicitly specify the name
>> of the color for each range in case of station data.
>>
>> This will be very easy if I know the exact name of each shade used in the
>> legend bar of wrf-contour (out of the 650 named colors in NCL). Is there a
>> way to print the names of these colors used in the legendbar?
>>
>> Thanks
>>
>> Tabish
>>
>> Tabish U Ansari
>> PhD student, Lancaster Environment Center
>> Lancaster Univeristy
>> Bailrigg, Lancaster,
>> LA1 4YW, United Kingdom
>>
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>
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