matplotlib-users Mailing List for matplotlib

> What is your matplotlib.__version__ ? I think that code only made it's
> way into v1.2.0 (the latest stable), and was did not make it into
> v1.1.1 (or anything before it)
I'm running 1.1.0 - I'll upgrade it now. Thanks for the help!
Oliver

On Wed, Dec 5, 2012 at 2:36 PM, Oliver King <oli...@gm...> wrote:
> What appears to be happening is that the alpha values in the cmap I use when I create the ListedColormap object are being ignored by the add_collection function. I see that this bug (or something quite like it) was reported in late 2008:
> http://matplotlib.1069221.n5.nabble.com/create-ListedColormap-with-different-alpha-values-tt18693.html#a18697
>
> Did the patch from late 2008 not make it into the code, or has this bug resurfaced? Does anyone know of a workaround for this issue?
It's all a blur now, but I don't think that patch made it in because
colormaps were inherently RGB not RGBA.
Something similar to that patch was merged in a year ago:
https://github.com/matplotlib/matplotlib/pull/660 and attached is the
result of running your code on my machine.
What is your matplotlib.__version__ ? I think that code only made it's
way into v1.2.0 (the latest stable), and was did not make it into
v1.1.1 (or anything before it)
--
Paul Ivanov
314 address only used for lists, off-list direct email at:
http://pirsquared.org | GPG/PGP key id: 0x0F3E28F7

Hi,
I've been trying to plot a line with varying alpha (but constant color). After much googling I have come up with the following code segment, which by all indications should work. It works when I vary an individual RGB element, but not when I vary alpha.
#################################################
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.collections import LineCollection
from matplotlib.colors import ListedColormap, BoundaryNorm
# the line to plot
x = np.linspace(0,1,101)
y = x*0.5-0.25
scaling = np.exp(-(x-0.5)**2/0.5**2) # scale the transparency of the line according to this
# Create a colormap which has a constant color, but varies the transparency.
N = 50 # this many different transparency levels
alpha_boundaries = np.linspace(np.min(scaling),np.max(scaling),N+1)
# The lowest values are transparent, the highest ones are opaque
cmap = ListedColormap([(0.0,0.0,0.0,a) for a in np.linspace(0,1,N)])
norm = BoundaryNorm(alpha_boundaries, cmap.N)
# Create a set of line segments so that we can color them individually
# This creates the points as a N x 1 x 2 array so that we can stack points
# together easily to get the segments. The segments array for line collection
# needs to be numlines x points per line x 2 (x and y)
points = np.array([x, y]).T.reshape(-1, 1, 2)
segments = np.concatenate([points[:-1], points[1:]], axis=1)
 
# Create the line collection object, setting the colormapping parameters.
# Have to set the actual values used for colormapping separately.
lc = LineCollection(segments, cmap=cmap, norm=norm)
lc.set_array(scaling)
ax = plt.subplot(111)
ax.add_collection(lc)
plt.xlim(x.min(), x.max())
plt.ylim(y.min(), y.max())
plt.show()
#################################################
What appears to be happening is that the alpha values in the cmap I use when I create the ListedColormap object are being ignored by the add_collection function. I see that this bug (or something quite like it) was reported in late 2008:
http://matplotlib.1069221.n5.nabble.com/create-ListedColormap-with-different-alpha-values-tt18693.html#a18697
Did the patch from late 2008 not make it into the code, or has this bug resurfaced? Does anyone know of a workaround for this issue?
Cheers,
Oliver

As of matplotlib v1.2.0 you can hatch a contour set directly. There is an
example in the gallery:
http://matplotlib.org/examples/pylab_examples/contourf_hatching.html
Hope that helps,
Phil
On 5 December 2012 17:28, spencerahill <spe...@gm...> wrote:
> Jae-Joon Lee wrote
> > On Thu, Sep 15, 2011 at 10:33 PM, Jonathan Slavin
> > &lt;
>
> > jslavin@.harvard
>
> > &gt; wrote:
> >> I'm wondering if there is some way to do cross hatching as a way to fill
> >> contours rather than colors (using contourf). The only references to
> >> cross hatching I see in the documentation are for patches type objects.
> >> As far as I can tell, contour and contourf return objects of their own
> >> type (contour.QuadContourSet) that do not have hatch as an attribute.
> >>
> >
> > Yes, it seems that hatching is only supported in patches.
> > You may workaround this by converting contours to multiple patches.
> > See the attachment.
> >
> > Matplotlib-users mailing list
>
> > Matplotlib-users@.sourceforge
>
> > https://lists.sourceforge.net/lists/listinfo/matplotlib-users
> >
> >
> > contour_to_hatched_patches.py (1K)
> > &lt;
> http://matplotlib.1069221.n5.nabble.com/attachment/23/0/contour_to_hatched_patches.py&gt
> ;
>
> Hi Jae-Joon,
>
> Your contour_to_hatched_patches.py script works excellently. Is there a way
> to suppress the contour lines and filling, leaving only stippling? I have
> been experimenting with it but no luck.
>
> I have a contourf of a 2D variable and a separate 2D array indicating
> regions of statistical significance (i.e. a mask, which equals 1 in cells
> where the variable is significant and equals 0 else), and I want to put
> black hatching over the contourf where it is significant. I can get this to
> work, but still with a black contour line surrounding the hatched region.
> I'd like to remove the line, leaving just the hatching. Thanks!
>
> Best,
> Spencer
>
>
>
>
> --
> View this message in context:
> http://matplotlib.1069221.n5.nabble.com/cross-hatching-in-contours-tp22p39945.html
> Sent from the matplotlib - users mailing list archive at Nabble.com.
>
>
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Jae-Joon Lee wrote
> On Thu, Sep 15, 2011 at 10:33 PM, Jonathan Slavin
> <
> jslavin@.harvard
> > wrote:
>> I'm wondering if there is some way to do cross hatching as a way to fill
>> contours rather than colors (using contourf). The only references to
>> cross hatching I see in the documentation are for patches type objects.
>> As far as I can tell, contour and contourf return objects of their own
>> type (contour.QuadContourSet) that do not have hatch as an attribute.
>>
> 
> Yes, it seems that hatching is only supported in patches.
> You may workaround this by converting contours to multiple patches.
> See the attachment.
> 
> Matplotlib-users mailing list
> Matplotlib-users@.sourceforge
> https://lists.sourceforge.net/lists/listinfo/matplotlib-users
> 
> 
> contour_to_hatched_patches.py (1K)
> <http://matplotlib.1069221.n5.nabble.com/attachment/23/0/contour_to_hatched_patches.py>
Hi Jae-Joon,
Your contour_to_hatched_patches.py script works excellently. Is there a way
to suppress the contour lines and filling, leaving only stippling? I have
been experimenting with it but no luck. 
I have a contourf of a 2D variable and a separate 2D array indicating
regions of statistical significance (i.e. a mask, which equals 1 in cells
where the variable is significant and equals 0 else), and I want to put
black hatching over the contourf where it is significant. I can get this to
work, but still with a black contour line surrounding the hatched region.
I'd like to remove the line, leaving just the hatching. Thanks!
Best,
Spencer
--
View this message in context: http://matplotlib.1069221.n5.nabble.com/cross-hatching-in-contours-tp22p39945.html
Sent from the matplotlib - users mailing list archive at Nabble.com.