Re: Centering GSN color bar

Hi Chad,

This is really useful! This example inspired me to create a new
examples page on how to set contour levels for use with symmetric
color tables, and I added your example to this. I modified it to use
the BlRe colormap, since I already had two examples using the BlueRed
color map.

http://www.ncl.ucar.edu/Applications/contoursym.shtml

Thanks for contributing! If anybody else has an example to contribute
to this page (or any other page for that matter), we love to hear from
you.

--Mary

On Apr 18, 2011, at 12:28 AM, Chad Herman wrote:

> I've often plotted grids where a large majority of the data was
> positive and the rest negative. To get the colormap to give the
> correct impression of the data, I would set the color bar to be
> symmetric so blue would be interpreted as cold or cooling and red as
> warm or warming. Sometimes the ratio of warm/cold was so large that
> the color bar extents were too large and suppressed a great deal of
> detail.
>
> I've figured out how to calculate the proper values of
> gsnSpreadColorStart and gsnSpreadColorEnd to ensure that negative
> values will be blue and positive values will be red. Attached is a
> demonstration of the gsnColorRange function. You can tweek the
> plotting limits to see how well the code correctly calculates the
> gsnColorStart/End values. Note that if the color bar spacing is
> larger than the value where you want blue to transition to red, the
> transition will not occur at the intended value because it's too
> small to resolve.
>
> Chad
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Received on Fri May 6 21:29:35 2011