matplotlib-users

[Matplotlib-users] colorbar for figure not mappable - zap edge lines

[James B. <bo...@ll...>]

I have a mesh of irregular polygons, like a finite element mesh. Each 
polygon has an associated value.
So, I have defined a color map with a appropriate normalization to 
define a color for each value and then
built a collection consisting of the polygon vertices and colors.
The resulting plot looks pretty good. This technique would seem to be 
useful for FE grids and Delaunay triangles.

Two questions:
(1) I want to attach a colorbar to the figure, but as of yet I have not 
worked out how to do it.
images such as scatter, imshow, pcolor are mappable and will accept a 
color bar but my simple polygon fill will not.

(2) How do I eliminate the edge lines about each polygon? I can make 
them very thin but a width of zero does not appear to work.
I recall this being discussed on the list, but now I cannot find the 
reference.

Thanks for any help.

--Jim

Re: [Matplotlib-users] colorbar for figure not mappable - zap edge lines

[Alan G I. <ai...@am...>]

On Wed, 12 Jan 2005, James Boyle apparently wrote: 
> (2) How do I eliminate the edge lines about each polygon? I can make
> them very thin but a width of zero does not appear to work.
> I recall this being discussed on the list, but now I cannot find the
> reference.

I recall John suggesting to also set the edge color (to the
same color, of course).  I hope a true zero width will
implemented.

However note that interpreting a linewidth of zero as a 1
pixel wide line is what PostScript does.  So the only way to
get a true zero width for PostScript output is to fill the
polygon without stroking it.

hth,
Alan Isaac

Re: [Matplotlib-users] colorbar for figure not mappable - zap edge lines

[James B. <bo...@ll...>]

To reply to my own post:
On question (1):
I modified the call to colorbar in pylab.py to accept a color map and 
norm keyword arguments. It was this functionality that was needed from 
the mappable image. So if the keywords are provided colorbar uses them, 
otherwise it looks for a mappable image.
This modification disables the observer feature for now if the color 
map is a keyword, a bit more work should get this going.
It looks like it would be easily doable, but I need something for the 
exigencies of work and will get back to this later.
This also would allow for a colorbar key for coloring contours and 
vectors.
I would also like to code up a floating color bar. Often I make 4/5 
images per page with a common colormap and normalization. It is
handy just to plop the reference colorbar in a central location not 
attached to a particular figure.

On question (2):
Alan Isaac pointed out that using the same edgecolor as the fillcolor 
would make the borders invisible.


--Jim

On Jan 12, 2005, at 12:55 PM, James Boyle wrote:

> I have a mesh of irregular polygons, like a finite element mesh. Each 
> polygon has an associated value.
> So, I have defined a color map with a appropriate normalization to 
> define a color for each value and then
> built a collection consisting of the polygon vertices and colors.
> The resulting plot looks pretty good. This technique would seem to be 
> useful for FE grids and Delaunay triangles.
>
> Two questions:
> (1) I want to attach a colorbar to the figure, but as of yet I have 
> not worked out how to do it.
> images such as scatter, imshow, pcolor are mappable and will accept a 
> color bar but my simple polygon fill will not.
>
> (2) How do I eliminate the edge lines about each polygon? I can make 
> them very thin but a width of zero does not appear to work.
> I recall this being discussed on the list, but now I cannot find the 
> reference.
>
> Thanks for any help.
>
> --Jim
>
>
>
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Re: [Matplotlib-users] colorbar for figure not mappable - zap edge lines

[John H. <jdh...@ac...>]

>>>>> "James" == James Boyle <bo...@ll...> writes:

    James> To reply to my own post: On question (1): I modified the
    James> call to colorbar in pylab.py to accept a color map and norm
    James> keyword arguments. It was this functionality that was

Perhaps it would be cleaner simply to derive a custom class from
ScalarMappable that does your fill calls and stores your cmap and norm
instances; then you would get the observer stuff for free.  If you
decide to go this route, perhaps you could submit the example.

    James> I would also like to code up a floating color bar. Often I
    James> make 4/5 images per page with a common colormap and
    James> normalization. It is handy just to plop the reference
    James> colorbar in a central location not attached to a particular
    James> figure.

I just committed changes to CVS to support this -- you can now place a
colorbar in a custom axes, and I added an orientation kwarg to
support horizontal or vertical colorbar layout.  Make sure you get
pylab.py revision 1.21 or later.

Here is an example

from pylab import *

ax = axes([0.1, 0.3, 0.8, 0.6])
im = imshow(rand(12,12), interpolation='nearest')

cax = axes([0.1, 0.1, 0.8, 0.15])
colorbar(cax=cax, orientation='horizontal')
show()

    James> On question (2): Alan Isaac pointed out that using the same
    James> edgecolor as the fillcolor would make the borders
    James> invisible.

Yep.

JDH