Re: [Matplotlib-users] question about levels & colormaps for contour functions

[Pablo R. <rom...@ho...>]

Eric,
the "BoundaryNorm" was what I was looking for.
it did exactly what I needed; split the colormap up evenly into discrete colors based on the number of elements in my levels array.
 
Thanks,
P.Romero

----------------------------------------
> Date: Sun, 15 Mar 2009 10:38:22 -1000
> From: ef...@ha...
> Subject: Re: [Matplotlib-users] question about levels & colormaps for contour functions
> To: rom...@ho...; mat...@li...
>
> Pablo Romero wrote:
>> Eric,
>>
>> I believe the problem is that my 19 levels are not evenly distributed;
>>
>> Lv=(1,3,5,6,7,8,9,10,12,14,16,18,20,25,30,35,40,50,75)
>
> No, I don't think that has much to do with it, unless the problem is
> that the colors of some levels are too similar.
>
> Again, please make a simple, complete, self-contained example, and we
> will go from there.
>
> I think what you want may be something like this:
>
> levs=[1,3,5,6,7,8,9,10,12,14,16,18,20,25,30,35,40,50,75]
> norm = mpl.colors.BoundaryNorm(levs, 256)
> z = rand(10,15)*14 # fake data covering only lower levs
> contourf(z, levs, norm=norm, cmap=cm.jet, extend='both')
> colorbar()
>
>
>>
>> the first part of the range starts at 1,3,5, but then includes 6,7,8,9, and then only goes with even numbers..10,12,14,16,18,20...then by 5 up until 35, then jumps by 10...etc.
>>
>> I know this seems strange, but this was done because Im plotting 'ocean wave heights' and these were decided to be the 'heights of interest' for the project Im working on.
>>
>
> Perfectly reasonable.
>
>> anyway, what I want is to be able to breakup the 'cm.jet' spectrum evenly based on the # of levels (and not on their values), and spread my levels evenly across the spectrum....
>>
>> i.e., I want the first 6-7 levels to be evenly spread from blue to about green acros cm.jet's spectrum, approx. the next 6 levels to be evenly spread across cm.jet's yellow-orange part of the spectrum, and the last few levels to be evenly spread across the reds...
>>
>> Ideally, Id like to be able to use any colormap, and simply break up its color spectrum evenly, and then assign each distinct color to each level in my levels array.
>>
>> So, I guess I need a method to programatically, evenly break up cm.jet by the # of levels, create a colors array & pass this array to contourf(colors='mycolorsarray')...
>>
>> does this make sense?
>>
>> P.Romero
>>
>> ----------------------------------------
>>> Date: Sun, 15 Mar 2009 08:32:32 -1000
>>> From: ef...@ha...
>>> Subject: Re: [Matplotlib-users] question about levels & colormaps for contour functions
>>> To: rom...@ho...
>>> CC: mat...@li...
>>>
>>> Pablo Romero wrote:
>>>> Hi,
>>>>
>>>> I would like to know how I can pass an array of levels and also a colormap to the contour() function and have the levels span the entire colormap. example...
>>>>
>>>> if I do the following....
>>>>
>>>>
>>>> Lv=(1,3,5,6,7,8,9,10,12,14,16,18,20,25,30,35,40,50,75)
>>>>
>>>> cs=plt.contourf(X,Y,waveheight,Lv,cmap=cm.jet,extend='both')
>>>>
>>>>
>>>> I would expect that contours that are in the higher levels (i.e., levels above value '14' in my levels array) would be plotted with lighter colors in the cm.jet spectrum; the greens, yellows,oranges,reds, etc.
>>>>
>>>> However, contourf is simply breaking up the lower,"dark blue" half of the cm.jet spectrum into small slices, and spreading all of my levels throughout only the bottom half of cm.jet.
>>>>
>>> I don't see the problem yet. Here is an attempt to recreate what it
>>> sounds like you are describing above (run in ipython -pylab):
>>>
>>> contourf(rand(10,12), arange(0,5.01,0.2), cmap=cm.jet, extend='both')
>>> colorbar()
>>>
>>> The data are all blue because they are in the 0-1 range, while the
>>> levels span the 0-5 range. The colorbar shows that the colormap is
>>> covering the latter range, as it should.
>>>
>>> If you can make a simple self-contained example like this, and then
>>> describe the difference between what it does and what you want it to do,
>>> we can figure out how to get your desired result.
>>>
>>> Eric
>>>
>>>
>>>
>>>
>>>
>>>> I followed this tutorial:
>>>> http://www.scipy.org/Cookbook/Matplotlib/ColormapTransformations
>>>>
>>>> that shows how to create a "discrete" colormap, but this also didnt work; the contourf function again simply sliced up the lower, blue colors and spread my all of my layers across the "blues" in my discrete colormap.
>>>>
>>>>
>>>> If I use a colors array instead of a colormap, I can achieve what I want. However, Id like to be able to use a colormap so that I dont have to manually create color arrays everytime that I want to change my colorscheme.
>>>>
>>>> So, how can I force contour() to spread my levels across THE WHOLE spectrum of a colormap?
>>>>
>>>> Please help,
>>>>
>>>> Thanks,
>>>> P.Romero
>>>>
>>>>
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