On 08/27/2010 07:15 AM, Ryan May wrote:
> On Thu, Aug 26, 2010 at 2:24 PM, Ben Edwards<bedwa...@cs.unm.edu> wrote:
>> Hello, I've used matplotlib for a while but never had cause to ask a
>> question until now. I am trying to add a patch to an axis, but would like
>> the patch to remain the same size when, interactively, I resize the
>> resulting figure. I am using TkAgg, and trying the following:
>>>>> import matplotlib.pyplot as plt
>>>>> import matplotlib.patches as patches
>>>>> ax = plt.gca()
>>>>> cp = patches.Circle((.5,.5),.025)
>>>>> ax.add_patch(cp)
>>>>> ax.set_aspect('equal')
>>>>> plt.draw()
>>>>> plt.show()
>> This gives me a nice blue circle in the middle of the plot, and using
>> ax.set_aspect('equal') I know that it will not be distorted into an ellipse.
>> But is there a way to ensure that when I make the Tk window bigger, that the
>> circle appears to be the same size as it was previously? I assume this would
>> entail some sort of transform, but I don't quite understand how they work...
>
> You can make the circle this way, specifying everything in axes coordinates:
>
> cp = patches.Circle((.5,.5),.025, transform=ax.transAxes)
>
> However, this puts the circle in the same spot in axes coordinates
> [(0.5,0.5) is the middle of the plot]. I'm not sure if that's what you
> want. I can't see any way to get Circle to use different transforms
> for the center and the size, so from here the only path forward I see
> is subclassing Circle. This way you could add code to the draw method
> to calculate the center in axes coordinates from the center in data
> coords. This needs to be done at draw time since the mapping of data
> coords->axes coords changes as you pan and zoom.
A simpler alternative is to use a CircleCollection with a single member.
Collections allow separate transforms for the patch and the offset;
the latter determines the location of the center.
Eric
>
> Ryan
>
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