Re: [Matplotlib-users] New contourf() drawing polygon boundaries for some reason?

[Michael D. <md...@st...>]

Thanks for the thorough investigation.

Michiel: can you look into why the macosx backend is drawing the strokes 
around the polygons?  Probably as simple as inadvertently ignoring an 
argument.

I'll look into the path simplification-related issues.

Cheers,
Mike

On 06/15/2009 03:29 PM, Zane Selvans wrote:
> Yes.  By far the worst of these behaviors is the macosx GUI output.  I
> could see the other ones just being the way it's supposed to look.
> Here's a summary:
>
> backend: macosx; path.simplify: (false|true) GUI =>  black borders to
> drawn polygons (incl. contour region crossing lines, very bad)
> http://zaneselvans.org/dropbox/contourf_backendmacosx.png
>
> backend: agg (PNG output) path.simplify: (true|false) =>  somewhat
> visible borders between polygons (esp. adjacent to contrasting colors)
> http://zaneselvans.org/dropbox/contourf_simplifytrue.png
> http://zaneselvans.org/dropbox/contourf_simplifyfalse.png
>
> backend: pdf (PDF output) path.simplify: true =>  reliably visible
> irregularities (but probably this is somewhat expected with SVG
> output)
> http://zaneselvans.org/dropbox/contourf_simplifytrue.pdf
>
> backend: pdf (PDF output) path.simplify: false =>  infinitessimally
> thin lines of background color visible between contour filled regions.
> http://zaneselvans.org/dropbox/contourf_simplifyfalse.pdf
>
> And here's what I used to generate them:
>
> def broken_contourf():
>      """
>      Simple demonstration that filled contour plots are broken.
>
>      Looking at the PDF and PNG output using the macosx backend, everything is
>      fine.  It's only the GUI output which is for some reason outlining the
>      polygons in the filled contours.
>
>      """
>      from numpy.random import uniform, seed
>      from matplotlib.mlab import griddata
>      import matplotlib.pyplot as plt
>      import numpy as np
>      # make up data.
>      #npts = int(raw_input('enter # of random points to plot:'))
>      seed(-1)
>      npts = 200
>      x = uniform(-2,2,npts)
>      y = uniform(-2,2,npts)
>      z = x*np.exp(-x**2-y**2)
>      # define grid.
>      xi = np.linspace(-2.1,2.1,100)
>      yi = np.linspace(-2.1,2.1,100)
>      # grid the data.
>      zi = griddata(x,y,z,xi,yi)
>      # contour the gridded data, plotting dots at the nonuniform data points.
>      CS = plt.contourf(xi,yi,zi,15,cmap=plt.cm.jet)
>      # plot data points.
>      plt.title('griddata() and contourf() test')
>      plt.savefig('broken_contourf.pdf')
>      plt.savefig('broken_contourf.png')
>
> On Fri, Jun 12, 2009 at 3:02 PM, Zane Selvans<za...@id...>  wrote:
>    
>> I switched back to using the macosx backend, and it turns out that the
>> thin black lines surrounding the polygons (including crossing the
>> filled contour regions from one closed contour to another) only get
>> displayed in the GUI.  PDF and PNG output look fine.
>>
>> Zane
>>
>> On Fri, Jun 12, 2009 at 2:27 PM, Zane Selvans<za...@id...>  wrote:
>>      
>>> If I set path.simplify: False, the shape of the gaps between the
>>> filled polygons does change.  Instead of being irregular, it becomes
>>> an infinitessimally thin gap of uniform width, allowing the (in this
>>> case white) background to show through.
>>>
>>> In both of these cases (path.simplify: True|False), the PNG version of
>>> the same figures also show representations of these gaps which are
>>> identical to those which appear in the PDF (though obviously
>>> pixelated), so I don't think it's something that's wrong in the vector
>>> graphics code per se.
>>>
>>> Zane
>>>
>>> On Fri, Jun 12, 2009 at 11:46 AM, Michael Droettboom<md...@st...>  wrote:
>>>        
>>>> Shot in the dark here, but what if you set the rcParam "path.simplify" to
>>>> False?  There have been recent changes to that code.
>>>>
>>>> Also, since the Agg backend doesn't have an associated GUI, you need to use
>>>> the savefig() command and provide a filename, rather than using show().
>>>>
>>>> Cheers,
>>>> Mike
>>>>
>>>> Zane Selvans wrote:
>>>>          
>>>>> Um, yeah.  So my response got bounced because of the attachment.  Take 2:
>>>>>
>>>>> For some reason my script bombed when I switched to the Agg backend,
>>>>> trying to display to the screen (it said Figure has no method show())
>>>>>
>>>>> So I output the plot as both a PDF and a PNG (still having backend:
>>>>> agg in my rcfile) and in both of those cases, irregular gaps are
>>>>> visible between the polygons making up the filled contours.  This
>>>>> wasn't the case with my previously installed setup.  It looks as if
>>>>> for some reason the vertices of the filled polygons are being
>>>>> calculated differently from different sides of the same contour,
>>>>> leading to overlap in some places, and gaps in others.  You can download
>>>>> the PDF version (in which the exact geometry is much clearer).
>>>>> from:
>>>>>
>>>>> http://zaneselvans.org/dropbox/LinDensity_Grid.pdf
>>>>>
>>>>> Zane
>>>>>
>>>>> On Fri, Jun 12, 2009 at 5:51 AM, Michael Droettboom<md...@st...>
>>>>> wrote:
>>>>>
>>>>>            
>>>>>> So you see this behavior if you switch to the Agg backend?  That's the
>>>>>> backend used to generate the images in the gallery.  If there's a
>>>>>> difference
>>>>>> there, that would seem to suggest some tweaking of the macosx backend
>>>>>> (which
>>>>>> is still relatively new) is in order.
>>>>>>
>>>>>> Mike
>>>>>>
>>>>>> Zane Selvans wrote:
>>>>>>
>>>>>>              
>>>>>>> I just installed the latest SciPy Superpack in order to get access to
>>>>>>> the scipy.spatial.KDTree class, and discovered that for some reason
>>>>>>> now when I use contourf() lines get drawn at the boundaries between
>>>>>>> the filled contours.  Additionally, there is always a single vertical
>>>>>>> line crossing from each contour boundary to the next.  I'm guessing
>>>>>>> that these are the edges of the filled polygons which are getting
>>>>>>> drawn.  This behavior doesn't seem to be consistent with the
>>>>>>> contourf() documentation and when I run code in griddata_demo.py it
>>>>>>> doesn't come out looking like the picture in the documentation/example
>>>>>>> gallery...
>>>>>>>
>>>>>>> Is anyone else seeing this behavior?  Is there a keyword I can use to
>>>>>>> force the edges of the polygons not to get drawn?
>>>>>>>
>>>>>>> This is on Mac OS X 10.5.7, with
>>>>>>> scipy.__version__ = 0.8.0.dev5635
>>>>>>> matplotlib.__version__ = 0.98.6svn
>>>>>>> numpy.__version__=1.4.0.dev6728
>>>>>>>
>>>>>>> As installed by superpack_2009.03.28.sh
>>>>>>> from http://macinscience.org/?page_id=6
>>>>>>>
>>>>>>> using:
>>>>>>> backend: macosx
>>>>>>>
>>>>>>> Cheers,
>>>>>>> Zane
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>                
>>>>>> --
>>>>>> Michael Droettboom
>>>>>> Science Software Branch
>>>>>> Operations and Engineering Division
>>>>>> Space Telescope Science Institute
>>>>>> Operated by AURA for NASA
>>>>>>
>>>>>>
>>>>>>
>>>>>>              
>>>>>
>>>>>
>>>>>            
>>>> --
>>>> Michael Droettboom
>>>> Science Software Branch
>>>> Operations and Engineering Division
>>>> Space Telescope Science Institute
>>>> Operated by AURA for NASA
>>>>
>>>>
>>>>          
>>>
>>> --
>>> Zane A. Selvans
>>> Amateur Earthling
>>> http://zaneselvans.org
>>> +1 303 815 6866
>>>
>>>        
>>
>> --
>> Zane A. Selvans
>> Amateur Earthling
>> http://zaneselvans.org
>> +1 303 815 6866
>>
>>      
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