matplotlib-users Mailing List for matplotlib

On 03/15/2011 11:47 AM, Tom Dimiduk wrote:
> Ah thanks.  I am used to the general math/physics convention of x axis
> being first.  Caught between conventions I guess.  Good to know why
> things are done differently.
>
> I am using the mouse click event.xdata and event.ydata as indexes into
> an array.  From what you say, it looks like I want to use
> im[im.shape[1]-y, x] to get the pixel a user clicked on.  Is that correct?

Almost--but mpl is using an inverted Y-axis so that the y-coordinate 
increases downward.  Therefore you need only im[round(y), round(x)].

Eric

>
> Thanks agaian,
> Tom
>
> On 03/15/2011 05:35 PM, Eric Firing wrote:
>> On 03/15/2011 10:23 AM, Tom Dimiduk wrote:
>>> It appears to me that when imshow tells you that the mouse cursor is at
>>> x=50, y=100
>>>
>>> That corresponds to array element
>>> im[100, 50]
>>>
>>> Is there a reason imshow does not have x be the first coordinate of the
>>> array as I would think of as conventional usage?
>>
>> That is not conventional usage.  Instead, for images, it common for the
>> image to correspond to a printout of memory, using the C convention.
>> Hence the column index is X, and incrementing the row index yields the
>> next line down on the page, thereby corresponding to a decrease in the Y
>> coordinate.
>>
>> Eric
>>
>>>
>>> Tom
>>
>> ------------------------------------------------------------------------------
>> Colocation vs. Managed Hosting
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>
> ------------------------------------------------------------------------------
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> A question and answer guide to determining the best fit
> for your organization - today and in the future.
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> _______________________________________________
> Matplotlib-users mailing list
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> https://lists.sourceforge.net/lists/listinfo/matplotlib-users

Ah thanks.  I am used to the general math/physics convention of x axis 
being first.  Caught between conventions I guess.  Good to know why 
things are done differently.

I am using the mouse click event.xdata and event.ydata as indexes into 
an array.  From what you say, it looks like I want to use
im[im.shape[1]-y, x] to get the pixel a user clicked on.  Is that correct?

Thanks agaian,
Tom

On 03/15/2011 05:35 PM, Eric Firing wrote:
> On 03/15/2011 10:23 AM, Tom Dimiduk wrote:
>> It appears to me that when imshow tells you that the mouse cursor is at
>> x=50, y=100
>>
>> That corresponds to array element
>> im[100, 50]
>>
>> Is there a reason imshow does not have x be the first coordinate of the
>> array as I would think of as conventional usage?
>
> That is not conventional usage.  Instead, for images, it common for the
> image to correspond to a printout of memory, using the C convention.
> Hence the column index is X, and incrementing the row index yields the
> next line down on the page, thereby corresponding to a decrease in the Y
> coordinate.
>
> Eric
>
>>
>> Tom
>
> ------------------------------------------------------------------------------
> Colocation vs. Managed Hosting
> A question and answer guide to determining the best fit
> for your organization - today and in the future.
> http://p.sf.net/sfu/internap-sfd2d
> _______________________________________________
> Matplotlib-users mailing list
> Mat...@li...
> https://lists.sourceforge.net/lists/listinfo/matplotlib-users

On 03/15/2011 10:23 AM, Tom Dimiduk wrote:
> It appears to me that when imshow tells you that the mouse cursor is at
> x=50, y=100
>
> That corresponds to array element
> im[100, 50]
>
> Is there a reason imshow does not have x be the first coordinate of the
> array as I would think of as conventional usage?

That is not conventional usage.  Instead, for images, it common for the 
image to correspond to a printout of memory, using the C convention. 
Hence the column index is X, and incrementing the row index yields the 
next line down on the page, thereby corresponding to a decrease in the Y 
coordinate.

Eric

>
> Tom

It appears to me that when imshow tells you that the mouse cursor is at
x=50, y=100

That corresponds to array element
im[100, 50]

Is there a reason imshow does not have x be the first coordinate of the 
array as I would think of as conventional usage?

Tom

Can you provide a standalone example?  This below is missing some 
imports and there are some mystery variables.

Mike

On 03/15/2011 12:25 PM, Auré Gourrier wrote:
> import matplotlib as mpl
> from matplotlib import pylab
> import numpy as np
>
> #build custom colormap
> cm_sym =customfunc()
>
> #define mesh grid
> theta = np.arange(0.,2.*math.pi+2.*math.pi/9,2.*math.pi/9)
> r = np.arange(0,1.1,0.1)
> X,Y = np.meshgrid(r,theta)
>
> #define rgba array
> polarcolorseq = mpl.cm.ScalarMappable(cmap=cm_hsvsym).to_rgba(Y)
> #set an increasing alpha value along the radius
> polarcolorseq[:,:,-1] = [list(np.arange(0,1.1,.1))]*10
>
> pylab.figure(figsize=(10,5),dpi=100,facecolor='white')
>
> #display using rectangular axis
> ax = pylab.subplot((121),axisbg='k')
> ax.imshow(np.flipud(np.swapaxes(polarcolorseq,0,1)))
>
> #display using polar axis
> ax2 = pylab.subplot((122),axisbg='k',projection='polar')    #also 
> tried with polar=True
> ax2.imshow(np.flipud(np.swapaxes(polarcolorseq,0,1)))
>
> pylab.draw()


-- 
Michael Droettboom
Science Software Branch
Space Telescope Science Institute
Baltimore, Maryland, USA

Really  no one to point me in the right direction ?
This is really important, I'm trying to wrap up a publication and this is the 
only element missing...




________________________________
De : Auré Gourrier <aur...@ya...>
À : mat...@li...
Envoyé le : Jeu 10 mars 2011, 15h 40min 04s
Objet : [Matplotlib-users] alternative to imshow with polar axes ?


Dear all,

Once again, I turn for help.
I'm trying to plot a polar image using colormap values for the theta values and 
increasing alpha values along the radius.
I do this using imshow passing the rgba tuple at each pixel position which works 
very nicely with rectangular axes, but fails to display using polar axes (see 
code below). 

As usual, I've done a fair bit of digging to find where the problem is and 
whether I could make out an alternate solution but haven't managed to come 
through. I've tried using pcolormesh but I don't see how to pass the rgba tuple
Can anyone point me in the right direction.
I'm using matplotlib 1.0.1 and Python 2.4

Cheers,

Auré

------
import matplotlib as mpl
from matplotlib import pylab
import numpy as  np

#build custom colormap
cm_sym =customfunc()

#define mesh grid
theta = np.arange(0.,2.*math.pi+2.*math.pi/9,2.*math.pi/9)
r = np.arange(0,1.1,0.1)
X,Y = np.meshgrid(r,theta)

#define rgba array
polarcolorseq = mpl.cm.ScalarMappable(cmap=cm_hsvsym).to_rgba(Y)
#set an increasing alpha value along the radius
polarcolorseq[:,:,-1] = [list(np.arange(0,1.1,.1))]*10

pylab.figure(figsize=(10,5),dpi=100,facecolor='white')

#display using rectangular axis
ax = pylab.subplot((121),axisbg='k')
ax.imshow(np.flipud(np.swapaxes(polarcolorseq,0,1)))

#display using polar axis
ax2 = pylab.subplot((122),axisbg='k',projection='polar')    #also tried with 
polar=True
ax2.imshow(np.flipud(np.swapaxes(polarcolorseq,0,1)))

pylab.draw()        


      

On 3/15/2011 8:51 AM, Michael Droettboom wrote:
> It has no way of deducing the file format from the file object.

Inspect f.name?

Alan Isaac

My fault, I didn't read the docstring properly. Thanks for both replies.

Best,

G

On 15/03/2011 13:51, Michael Droettboom wrote:
> It has no way of deducing the file format from the file object.
>
> You need to explicitly pass the format keyword to savefig, e.g.:
>
>     savefig(f, format='pdf')
>
> Mike
>
> On 03/15/2011 07:11 AM, Giovanni Luca Ciampaglia wrote:
>> Hi all,
>> I call savefig by passing to it a file-like object but it appears to not
>> get the graphics format right:
>>
>> f = open('not_a_pdf.pdf', 'w')
>> plot([1,2,3])
>> savefig(f)
>>
>> but it produces a PNG image. Can anybody confirm this? I am on
>> matplotlib 0.99.3
>>
>> Cheers,
>>
>> Giovanni
>>
>> ------------------------------------------------------------------------------
>> Colocation vs. Managed Hosting
>> A question and answer guide to determining the best fit
>> for your organization - today and in the future.
>> http://p.sf.net/sfu/internap-sfd2d
>> _______________________________________________
>> Matplotlib-users mailing list
>> Mat...@li...
>> https://lists.sourceforge.net/lists/listinfo/matplotlib-users
>>
>

It has no way of deducing the file format from the file object.

You need to explicitly pass the format keyword to savefig, e.g.:

   savefig(f, format='pdf')

Mike

On 03/15/2011 07:11 AM, Giovanni Luca Ciampaglia wrote:
> Hi all,
> I call savefig by passing to it a file-like object but it appears to not
> get the graphics format right:
>
> f = open('not_a_pdf.pdf', 'w')
> plot([1,2,3])
> savefig(f)
>
> but it produces a PNG image. Can anybody confirm this? I am on
> matplotlib 0.99.3
>
> Cheers,
>
> Giovanni
>
> ------------------------------------------------------------------------------
> Colocation vs. Managed Hosting
> A question and answer guide to determining the best fit
> for your organization - today and in the future.
> http://p.sf.net/sfu/internap-sfd2d
> _______________________________________________
> Matplotlib-users mailing list
> Mat...@li...
> https://lists.sourceforge.net/lists/listinfo/matplotlib-users
>    


-- 
Michael Droettboom
Science Software Branch
Space Telescope Science Institute
Baltimore, Maryland, USA

Hi all,
I call savefig by passing to it a file-like object but it appears to not 
get the graphics format right:

f = open('not_a_pdf.pdf', 'w')
plot([1,2,3])
savefig(f)

but it produces a PNG image. Can anybody confirm this? I am on 
matplotlib 0.99.3

Cheers,

Giovanni

Hi all,
I call savefig by passing to it a file-like object but it appears to not 
get the graphics format right:

f = open('not_a_pdf.pdf', 'w')
plot([1,2,3])
savefig(f)

but it produces a PNG image. Can anybody confirm this? I am on 
matplotlib 0.99.3

Cheers,
-- 
Giovanni L. Ciampaglia
PhD Student
University of Lugano, MACS Lab

I'm plotting a series of sub plots within a figure, where most are small sub
plots, but the last one spans the width of the figure. For the final subplot
only, I want to set the xtick pad to 20. Something like:


import matplotlib.pyplot as plt

fig = plt.figure()
ax1 = fig.add_subplot(2,2,1)
ax2 = fig.add_subplot(2,2,2)
ax3 = fig.add_subplot(2,1,3)


plt.setp(ax3.xaxis.get_major_ticks(), pad=20)
plt.show()

But this doesn't have any effect on the final plot.  I've also tried getting
the ticks individually and calling set_pad(20) i.e.:

for tick in ax3.xaxis.get_major_ticks():
    tick.set_pad(20)

But this does't work either. Anyone have an ideas?


-- 
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