matplotlib

On Mon, Aug 22, 2005 at 12:55:16PM -1000, Eric Firing wrote:
> (from phil:)
.... stuff deleted ......
> 
> Phil, Jeff,
> 
> Yes, the present colorbar is designed for use with images, not with 
> contourf, and fixing it (or making a new one) is something I have wanted 
> to do for quite a while.  I just haven't gotten to it yet.  Prompted by 
> your two emails, maybe I can at least take a close look during the next 
> week to see what it would take.  It might be easy--probably is.  No 
> promises yet, though.
> 
> Eric

Thanks Eric,

I also believe it should be easy to do. But it is better done by
somebody more familiar with matplotlib and python than I. I have
written such codes for other languages but need more practice before
I could do it elegantly in python.

As long as you are digging around in there, can I have you think about
another couple features? 

1) The best colorbars in my mind have "triangles" at the endpoints
that indicate the color for the region higher than the highest
contour, and lower than the lowest contours. This allows one to label
only the meaningful boundaries and not specify how much above or below
those regions.

2) I frequently need to set contour intervals (the filled region
boundaries) to be approximately logarithmic. But I dont want to have
these filled regions occupy a fraction of the colorbar proportional to
their fraction of the total interval. I want each region  to be equal
area on the colorbar. 

An example of these features can be seen in the attached PNG figure
that I created in Yorick with a colorbar code I wrote. I havent tried
for beauty, but these figure are OK for for working plots. You can see
the point for the unequal contour intervals in the difference plot at
the bottom.

For the codes I wrote this necessitated supplying arguments to the
colorbar function like....

colorbar(levs, colors)
where levels was an N element array, and colors was an N+1 element
list containing color info for each filled region. 

Thanks for listening.

Phil

Phil Rasch wrote:
> On Mon, Aug 22, 2005 at 12:55:16PM -1000, Eric Firing wrote:
> 
>>(from phil:)
> 
> .... stuff deleted ......
> 
>>Phil, Jeff,
>>
>>Yes, the present colorbar is designed for use with images, not with 
>>contourf, and fixing it (or making a new one) is something I have wanted 
>>to do for quite a while.  I just haven't gotten to it yet.  Prompted by 
>>your two emails, maybe I can at least take a close look during the next 
>>week to see what it would take.  It might be easy--probably is.  No 
>>promises yet, though.
>>
>>Eric
> 
> 
> Thanks Eric,
> 
> I also believe it should be easy to do. But it is better done by
> somebody more familiar with matplotlib and python than I. I have
> written such codes for other languages but need more practice before
> I could do it elegantly in python.
> 
> As long as you are digging around in there, can I have you think about
> another couple features? 
> 
> 1) The best colorbars in my mind have "triangles" at the endpoints
> that indicate the color for the region higher than the highest
> contour, and lower than the lowest contours. This allows one to label
> only the meaningful boundaries and not specify how much above or below
> those regions.
> 
> 2) I frequently need to set contour intervals (the filled region
> boundaries) to be approximately logarithmic. But I dont want to have
> these filled regions occupy a fraction of the colorbar proportional to
> their fraction of the total interval. I want each region  to be equal
> area on the colorbar. 
> 
> An example of these features can be seen in the attached PNG figure
> that I created in Yorick with a colorbar code I wrote. I havent tried
> for beauty, but these figure are OK for for working plots. You can see
> the point for the unequal contour intervals in the difference plot at
> the bottom.
> 
> For the codes I wrote this necessitated supplying arguments to the
> colorbar function like....
> 
> colorbar(levs, colors)
> where levels was an N element array, and colors was an N+1 element
> list containing color info for each filled region. 
> 
> Thanks for listening.
> 
> Phil
>

Phil,

> 
> As long as you are digging around in there, can I have you think about
> another couple features? 

OK.


> 
> An example of these features can be seen in the attached PNG figure

I think you forgot to attach the figure--I didn't see it.  Your 
description is pretty clear, though.

Eric

Just for completness I will attach the figure this time.

Phil

On Mon, Aug 22, 2005 at 02:02:57PM -1000, Eric Firing wrote:
> Phil Rasch wrote:
> >On Mon, Aug 22, 2005 at 12:55:16PM -1000, Eric Firing wrote:
> >
> >>(from phil:)
> >
> >.... stuff deleted ......
> >
> >>Phil, Jeff,
> >>
> >>Yes, the present colorbar is designed for use with images, not with 
> >>contourf, and fixing it (or making a new one) is something I have wanted 
> >>to do for quite a while.  I just haven't gotten to it yet.  Prompted by 
> >>your two emails, maybe I can at least take a close look during the next 
> >>week to see what it would take.  It might be easy--probably is.  No 
> >>promises yet, though.
> >>
> >>Eric
> >
> >
> >Thanks Eric,
> >
> >I also believe it should be easy to do. But it is better done by
> >somebody more familiar with matplotlib and python than I. I have
> >written such codes for other languages but need more practice before
> >I could do it elegantly in python.
> >
> >As long as you are digging around in there, can I have you think about
> >another couple features? 
> >
> >1) The best colorbars in my mind have "triangles" at the endpoints
> >that indicate the color for the region higher than the highest
> >contour, and lower than the lowest contours. This allows one to label
> >only the meaningful boundaries and not specify how much above or below
> >those regions.
> >
> >2) I frequently need to set contour intervals (the filled region
> >boundaries) to be approximately logarithmic. But I dont want to have
> >these filled regions occupy a fraction of the colorbar proportional to
> >their fraction of the total interval. I want each region  to be equal
> >area on the colorbar. 
> >
> >An example of these features can be seen in the attached PNG figure
> >that I created in Yorick with a colorbar code I wrote. I havent tried
> >for beauty, but these figure are OK for for working plots. You can see
> >the point for the unequal contour intervals in the difference plot at
> >the bottom.
> >
> >For the codes I wrote this necessitated supplying arguments to the
> >colorbar function like....
> >
> >colorbar(levs, colors)
> >where levels was an N element array, and colors was an N+1 element
> >list containing color info for each filled region. 
> >
> >Thanks for listening.
> >
> >Phil
> >

-- 
Phil Rasch, Climate Modeling Section, National Center for Atmospheric Research
Mail     --> P.O. Box 3000, Boulder CO 80307  
Shipping --> 1850 Table Mesa Dr, Boulder, CO 80305
email: pjr@..., Web: http://www.cgd.ucar.edu/cms/pjr Phone: 303-497-1368, FAX: 303-497-1324

Eric Firing wrote:

>
>>
>> Thanks Eric - I just wanted to make sure I wasn't missing some 
>> obvious way to do it.
>
>
>
> Jeff,
>
> A possible trick would be to make a very skinny subplot (using custom 
> sizing and positioning) and use contourf itself to make the colorbar 
> in it.  I think this is actually the way I am doing it in Matlab.  (A 
> colleague and I greatly customized the Matlab colorbar for this sort 
> of thing a long time ago.)
>
> Eric


Eric/Phil:  Here is a hack that produces colorbars with discrete contour 
intervals for use with contourf.  It's in the form of a patch for 
pylab.py and figure.py (based on 0.83.2).  When pylab.colorbar is 
called, it checks to see if the current image was created by contourf, 
and if so calls figure.colobar_contourf (which uses contourf instead of 
imshow to make the colorbar).  Here's a test script:

"""test script for contourf colorbar"""
from pylab import *
def func3(x,y):
    return (1- x/2 + x**5 + y**3)*exp(-x**2-y**2)
dx, dy = 0.05, 0.05
X,Y = meshgrid(arange(-3.0,3.0001,dx),arange(-3.0,3.0001,dy))
Z = func3(X, Y)
levels = linspace(-1.2,1.2,13)
l,c = contour (X, Y, Z, levels, linewidths=0.5, colors='k')
clabel(c,l,fmt='%4.2f')
l,c = contourf(X, Y, Z, levels, cmap=cm.jet)
colorbar(tickfmt='%4.2f',orientation='horizontal') # horiz colorbar
colorbar(tickfmt='%4.2f',orientation='vertical') # vert colorbar
axis([-3,3,-3,3])
show()


This doesn't address the other two of Phil's requests (triangles at the 
ends, and constant intervals on the colorbar for non-constant contour 
levels), but I think it's a start.

-Jeff

-- 
Jeffrey S. Whitaker         Phone  : (303)497-6313
Meteorologist               FAX    : (303)497-6449
NOAA/OAR/CDC  R/CDC1        Email  : Jeffrey.S.Whitaker@...
325 Broadway                Office : Skaggs Research Cntr 1D-124
Boulder, CO, USA 80303-3328 Web    : http://tinyurl.com/5telg