Re: [matplotlib-devel] Transforms bug

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

I'm not sure this is a bug.  The transformation is being applied in data 
space, and then the mapping to physical space is not square in the x and 
y dimensions.

I think calling set_aspect('equal') on the axes should fix this -- if it 
doesn't, that's indeed a bug.

Mike

On 08/27/2012 01:05 PM, Damon McDougall wrote:
> My cherubs,
>
> With my new found free time, I may have discovered a sneaky bug to which
> you are not aware. Unless, of course, my example code is incorrect.
>
> I do normal setup:
>
> from matplotlib.backends.backend_pdf import FigureCanvasPdf as FigureCanvas
> from matplotlib.figure import Figure
> from matplotlib.patches import Rectangle
> from matplotlib.transforms import Affine2D
>
> fig = Figure()
> canvas = FigureCanvas(fig)
> ax = fig.add_subplot(1, 1, 1)
>
> # Make a sexy rectangle at the origin
> r = Rectangle((0.0, 0.0), 0.6, 0.4)
>
> # Construct a mind-blowing transformation: rotation by 30 degrees
> t = Affine2D().rotate_deg(30.0)
>
> # Make sure to add in the already-known axes data transformation
> t += ax.transData
>
> # Rotate that shizzle
> r.set_transform(t)
>
> # Plottify
> ax.add_patch(r)
>
> fig.savefig('my_awesome_TRAPEZIUM.pdf')
>
> Or you can look at my output here: http://i.imgur.com/2l439.png
>
> Rotation by 30 degrees is an angle-preserving linear transformation. So
> this shouldn't happen.
>
> Here's what's messing shiz up: the figure dimensions are not square.
> Look what happens when I use a square figure and make the axes fit
> exactly to the figure dimensions:
>
> ...
> fig = Figure((4, 4))
> ...
> ax = fig.add_axes([0, 0, 1, 1])
> ...
> ...
> fig.savefig('my_awesome_RECTANGLE.pdf')
>
> You can see the output here: http://i.imgur.com/baXiH.png
>
> Boom.
>
> I have no idea how to fix it. I came across it while trying to address
> https://github.com/matplotlib/matplotlib/issues/987 but it may or may
> not also be related to
> https://github.com/matplotlib/matplotlib/issues/1113
>
> Let me know if it's worth putting in github issue. I'm dont want to
> create a duplicate ticket should it transpire that this problem is
> actually #1113 in disguise.
>
> Best,
> Damon
>