Yannick Copin wrote:
> Hi,
>
> I would like to plot lots of error ellipses on my plot. I thought I
> could use an EllipseCollection to do so, but I didn't manage to get the
> ellipse sizes, expressed in data units, right (see test script attached).
>
> When using a plain list of Ellipse's, everything looks fine:
>
> ells = [ P.matplotlib.patches.Ellipse(xy=xyi,
> width=wi, height=hi,
> angle=ai,
> edgecolor='b',
> facecolor='b',
> alpha=0.3)
> for xyi,wi,hi,ai in zip(xy,w,h,a)]
> for ell in ells:
> ax.add_artist(ell)
>
> But when using EllipseCollection (as explained in
> http://matplotlib.sourceforge.net/examples/pylab_examples/ellipse_collection.html),
>
>
> coll = P.matplotlib.collections.EllipseCollection(widths=w,
> heights=h,
> angles=a,
> units='x',
> offsets=xy,
> transOffset=ax.transData,
> edgecolor='r',
> facecolor='r',
> alpha=0.3)
> ax.add_collection(coll)
>
> the size of the ellipses (expressed in data units) appears incorrect,
> and depends furthermore of the aspect ratio of the figure (try pan/zoom
> or resize the interactive window).
Maybe I am misunderstanding, but the EllipseCollection in the example is
panning and zooming as I expect. The shapes and orientations are
staying the same while the scale expands and contracts with the x-axis.
The problem is that the option you are looking for does not exist yet.
I am not sure yet whether what you need is identical to an option I
added to quiver (from which I partially derived EllipseCollection). I
suspect it is.
Do you want width to scale with x and height to scale with y? And the
angle to scale such that a 45-degree angle always corresponds to equal
increments in x and in y, all in data units?
>
> I naively thought the two approaches should give the same result... Did
> I miss something in the way to use EllipseCollections?
EllipseCollection is derived more from quiver than from Ellipse.
Eric
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