matplotlib-users

[Matplotlib-users] fill area between two curves? fill_between?

[<rep...@we...>]

I want to fill the area between two curves with a color (incl. alpha channel, I use the agg backend). fill() seems to fill only the area between the x-axis and one curve - at least I found no way for filling only the area between two graphs. Is there a way for doing so at all? Or do I have to use another graphic library for this kind of fill_between()?

-Dirk
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Re: [Matplotlib-users] fill area between two curves? fill_between?

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

>>>>> "Dirk" ==   <rep...@we...> writes:

    Dirk> I want to fill the area between two curves with a color
    Dirk> (incl. alpha channel, I use the agg backend). fill() seems
    Dirk> to fill only the area between the x-axis and one curve - at
    Dirk> least I found no way for filling only the area between two
    Dirk> graphs. Is there a way for doing so at all? Or do I have to
    Dirk> use another graphic library for this kind of fill_between()?

All of the matplotlib plot commands create primitive objects
(lines.Line2D, patches.Rectangle, patches.Polygon, text.Text).  If a
plot command doesn't suit your needs, you can roll your own by
creating the right kind of primitive object.  Here is a fill_between
implementation

from matplotlib.matlab import *
from matplotlib.patches import Polygon

def fill_between(ax, x, y1, y2, **kwargs):
    # add x,y2 in reverse order for proper polygon filling
    verts = zip(x,y1) + [(x[i], y2[i]) for i in range(len(x)-1,-1,-1)]
    poly = Polygon(verts, **kwargs)
    ax.add_patch(poly)
    ax.autoscale_view()
    return poly

x = arange(0, 2, 0.01)
y1 = sin(2*pi*x)
y2 = sin(4*pi*x) + 2
ax = gca()

p = fill_between(ax, x, y1, y2, facecolor='g')
p.set_alpha(0.5)
show()
                 
Hope this helps,
JDH

Re: [Matplotlib-users] fill area between two curves? fill_between?

[Andrew S. <str...@as...>]

On Sep 28, 2004, at 5:15 AM, John Hunter wrote:

>>>>>> "Dirk" ==   <rep...@we...> writes:
>
>     Dirk> I want to fill the area between two curves with a color
>     Dirk> (incl. alpha channel, I use the agg backend). fill() seems
>     Dirk> to fill only the area between the x-axis and one curve - at
>     Dirk> least I found no way for filling only the area between two
>     Dirk> graphs. Is there a way for doing so at all? Or do I have to
>     Dirk> use another graphic library for this kind of fill_between()?
>
> All of the matplotlib plot commands create primitive objects
> (lines.Line2D, patches.Rectangle, patches.Polygon, text.Text).  If a
> plot command doesn't suit your needs, you can roll your own by
> creating the right kind of primitive object.  Here is a fill_between
> implementation

The fill() command itself does work if you give it coordinates for a 
closed polygon.  This draws a filled spiral:

from matplotlib.matlab import *
from numarray import *

theta = arange(0,8*pi,0.1)
a=1
b=.2

for dt in arange(0,2*pi,pi/2.0):

     x = a*cos( theta+dt )*exp(b*theta)
     y = a*sin( theta+dt )*exp(b*theta)

     dt = dt+pi/4.0

     x2 = a*cos( theta+dt )*exp(b*theta)
     y2 = a*sin( theta+dt )*exp(b*theta)

     xf = concatenate( (x,x2[::-1]) )
     yf = concatenate( (y,y2[::-1]) )

     p1=fill(xf,yf)

show()

Re: [Matplotlib-users] fill area between two curves? fill_between?

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

>>>>> "Andrew" == Andrew Straw <str...@as...> writes:

    Andrew> The fill() command itself does work if you give it
    Andrew> coordinates for a closed polygon.  This draws a filled
    Andrew> spiral:

Of course (slaps self on forehead).  So my example rewritten would be
rewritten using the cleaner

    from matplotlib.matlab import *

    x1 = arange(0, 2, 0.01)
    y1 = sin(2*pi*x1)
    y2 = sin(4*pi*x1) + 2

    # reverse x and y2 so the polygon fills in order
    x = concatenate( (x1,x1[::-1]) )
    y = concatenate( (y1,y2[::-1]) )

    p = fill(x, y, facecolor='g')
    set(p, alpha=0.5)
    show()

I took the liberty of adding your example to CVS in the examples
subdir as examples/fill_spiral.py.  

Thanks!
JDH

Re: [Matplotlib-users] fill area between two curves? fill_between?

[<rep...@we...>]

John Hunter: Normally I wouldn't waste bandwith in a mailing-list by sending
neither a question nor an answer, but in this case I feel the urge to thank
you for your support. Your function does exactly what I need and you even
gave a hint on how to implement such functional extensions. On top of that,
the answer came an hour after I sent the question :-)

> All of the matplotlib plot commands create primitive objects
> (lines.Line2D, patches.Rectangle, patches.Polygon, text.Text).  If a
> plot command doesn't suit your needs, you can roll your own by
> creating the right kind of primitive object. [...]

Do I have to dive into the class description at
http://matplotlib.sourceforge.net/classdocs.html to get this informations or
is there a more user-friendly description of the matplotlib internals?

Thanks
Dirk


----- Original Message -----
From: "John Hunter" <jdh...@ac...>
To: <rep...@we...>
Cc: <mat...@li...>
Sent: Tuesday, September 28, 2004 2:15 PM
Subject: Re: [Matplotlib-users] fill area between two curves? fill_between?


> >>>>> "Dirk" ==   <rep...@we...> writes:
>
>     Dirk> I want to fill the area between two curves with a color
>     Dirk> (incl. alpha channel, I use the agg backend). fill() seems
>     Dirk> to fill only the area between the x-axis and one curve - at
>     Dirk> least I found no way for filling only the area between two
>     Dirk> graphs. Is there a way for doing so at all? Or do I have to
>     Dirk> use another graphic library for this kind of fill_between()?
>
> All of the matplotlib plot commands create primitive objects
> (lines.Line2D, patches.Rectangle, patches.Polygon, text.Text).  If a
> plot command doesn't suit your needs, you can roll your own by
> creating the right kind of primitive object.  Here is a fill_between
> implementation
>
> from matplotlib.matlab import *
> from matplotlib.patches import Polygon
>
> def fill_between(ax, x, y1, y2, **kwargs):
>     # add x,y2 in reverse order for proper polygon filling
>     verts = zip(x,y1) + [(x[i], y2[i]) for i in range(len(x)-1,-1,-1)]
>     poly = Polygon(verts, **kwargs)
>     ax.add_patch(poly)
>     ax.autoscale_view()
>     return poly
>
> x = arange(0, 2, 0.01)
> y1 = sin(2*pi*x)
> y2 = sin(4*pi*x) + 2
> ax = gca()
>
> p = fill_between(ax, x, y1, y2, facecolor='g')
> p.set_alpha(0.5)
> show()
>
> Hope this helps,
> JDH
>

Re: [Matplotlib-users] fill area between two curves? fill_between?

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

>>>>> "Dirk" ==   <rep...@we...> writes:

    Dirk> John Hunter: Normally I wouldn't waste bandwith in a
    Dirk> mailing-list by sending neither a question nor an answer,
    Dirk> but in this case I feel the urge to thank you for your
    Dirk> support. Your function does exactly what I need and you even
    Dirk> gave a hint on how to implement such functional
    Dirk> extensions. On top of that, the answer came an hour after I
    Dirk> sent the question :-)

Your welcome...  

    Dirk> Do I have to dive into the class description at
    Dirk> http://matplotlib.sourceforge.net/classdocs.html to get this
    Dirk> informations or is there a more user-friendly description of
    Dirk> the matplotlib internals?

I think the best way, after studying the examples in the examples
directory of the src distribution, is to read through the code in
axes.py.  Almost all  of the plotting functions in matplotlib.matlab
are wrappers for axes plotting functions.  Eg scatter wraps
matplotlib.Axes.scatter, plot wraps matplotlib.Axes.plot and so on.
Most of the axes plotting functions in turn create the primitive
objects that actually make up the plot.  Axes.plot is one of the more
complicated functions, since it does a lot of variable length argument
processing, so it is probably not the best place to start.  

If you have a link to the classdocs open, as you read through the axes
code, you can read the docs for the functions that are being called.

JDH           

Re: [Matplotlib-users] fill area between two curves? fill_between?

[<fcc...@fi...>]

On Tuesday 28 September 2004 16:48, John Hunter wrote:
> >>>>> "Dirk" ==   <rep...@we...> writes:
>
>     Dirk> John Hunter: Normally I wouldn't waste bandwith in a
>     Dirk> mailing-list by sending neither a question nor an answer,
>     Dirk> but in this case I feel the urge to thank you for your
>     Dirk> support. Your function does exactly what I need and you even
>     Dirk> gave a hint on how to implement such functional
>     Dirk> extensions. On top of that, the answer came an hour after I
>     Dirk> sent the question :-)
>
> Your welcome...

Hi John, 

I agree with Dirk on the precision and promptness of your responses to all our 
questions. I am always learning new things about matplolib (MPL) through 
theses Q&A exchanges. But since topic of bandwidth usage came up in this 
thread, for the sake of saving not only Sourceforge's but also JDH's 
bandwidth, I believe a documentation project for MPL should be started. I 
understand that you might not want to commit effort to document MPL now, 
since it's still under pretty intense development. However, starting a Wiki 
documentation project might be a good idea, since the user community could 
help by adding short tutorials  and recipes derived from their own experience 
with MPL. Moreover, the wiki could slowly evolve into a full blown 
documentation project.

What do you think?

cheers,

 Flavio
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