jason-s...@creativetrax.com wrote:
> A couple of us are trying to figure out how to scale arrows in a quiver
> plot so that we can exactly specify what the output arrows look like.
> For example, we'd like to scale the vectors to half of their size, and
> have it look like that on the quiver plot.
>
> So I tried even just getting a quiver plot to plot an arrow exactly as I
> passed it, without it scaling anything. My attempt is this:
>
> import matplotlib.pylab as plt
> fig=plt.figure(figsize=[6,6])
> q=plt.quiver([0],[0],[1],[1],units='x',scale=1,angles='xy')
I have committed a change to svn trunk, so that if you change the
above to
q = plt.quiver([0],[0], [1], [1], scale_units='xy', angles='xy', scale=1)
it should do exactly what you want. When scale_units is given, the
setting of "units" controls only the specification of the arrow width,
so if you are not specifying the width, it doesn't have any effect.
If I could start from scratch, I probably could come up with a better
set of kwarg names and defaults; but for reasons of
backwards-compatibility, this is what we have. The new scale_units
kwarg makes it much easier to manually set the scale. Previously (and
still with the default of scale_units=None), it was almost hopelessly
confusing.
(Maybe I should add "width_units", identical to "units", and deprecate
the latter; this might make the meanings of the kwargs clearer.)
Eric
> ax=plt.axis([0,1.5,0,1.5])
> plt.grid(True)
> plt.savefig('test.png')
>
> I'm trying to get the arrow to go from (0,0) to (1,1). However, with
> units='x', it's just short, and with units='y', it's just a bit too
> long. Furthermore, if I don't make the aspect ratio equal to one, I get
> wild results since the x-axis and y-axis are different units then. It
> would be really nice if there was a way to say units='data' (for data
> coordinates), and then if scale=1, the arrows would be drawn with the
> heads and tails at exactly the passed points. If scale=2, then each
> arrow would be drawn exactly half of its length. I realize that
> units='data' might mess up the other measurements of an arrow, though,
> so maybe another parameter is called for, like a scale_units, that
> defaults to units.
>
> What do people think?
>
> Thanks,
>
> Jason
>
>
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