Hi again,
I found an example that implements something like I described:
http://matplotlib.sourceforge.net/examples/pylab_examples/anchored_artists.html?highlight=size%20bar
However, it did not allow to set arbitrary position. I modified the example to
provide the anchor_to_bbox argument of AnchoredOffsetbox that allows to set the
scale bars position in axes coordinates. The big gotcha is that you have to
provide the loc argument to fix the that point should be adjusted to the
coordinates (1 for upper right, 2 for upper left, see the docs of legend for
all the codes). This is not clear in the documentation.
In the example attached, I add two scalebars: vertical and horizontal that
cross at the lower right corner.
Bartosz
from matplotlib.patches import Rectangle, Ellipse
from matplotlib.offsetbox import AnchoredOffsetbox, AuxTransformBox, VPacker,\
TextArea, HPacker
import matplotlib.pyplot as plt
class XSizeBar(AnchoredOffsetbox):
def __init__(self, pos, size, label, loc, ax=None,
pad=0.1, borderpad=0.1, sep=2, prop=None, frameon=True):
"""
Draw a horizontal bar with the size in data coordinate of the give axes.
A label will be drawn underneath (center-alinged).
pad, borderpad in fraction of the legend font size (or prop)
sep in points.
"""
if not ax:
ax = plt.gca()
self.size_bar = AuxTransformBox(ax.transData)
self.size_bar.add_artist(Rectangle((0,0), size, 0, fc="none"))
self.txt_label = TextArea(label, minimumdescent=False)
self._box = VPacker(children=[self.size_bar, self.txt_label],
align="center",
pad=0, sep=sep)
AnchoredOffsetbox.__init__(self, loc, pad=pad, borderpad=borderpad,
child=self._box,
prop=prop,
bbox_to_anchor=pos,
bbox_transform=ax.transAxes,
frameon=frameon)
class YSizeBar(AnchoredOffsetbox):
def __init__(self, pos, size, label, loc, ax=None,
pad=0.1, borderpad=0.1, sep=2, prop=None, frameon=True):
if not ax:
ax = plt.gca()
self.size_bar = AuxTransformBox(ax.transData)
self.size_bar.add_artist(Rectangle((0,0), 0, size, fc="none"))
self.txt_label = TextArea(label, minimumdescent=False)
self._box = HPacker(children=[self.size_bar, self.txt_label],
align="center",
pad=0, sep=sep)
AnchoredOffsetbox.__init__(self, loc, pad=pad, borderpad=borderpad,
child=self._box,
prop=prop,
bbox_to_anchor=pos,
bbox_transform=ax.transAxes,
frameon=frameon)
if __name__ == "__main__":
ax = plt.gca()
ax.set_aspect(1.)
# draw a horizontal bar with length of 0.1 in Data coordinate
# (ax.transData) with a label underneath.
x_asb = XSizeBar((0.9,0.1),
0.1,
r"1 s",
loc=1,
pad=0., borderpad=0., sep=5,
frameon=False)
y_asb = YSizeBar((0.9,0.1),
0.1,
r"1 V",
loc=3,
pad=0., borderpad=0., sep=5,
frameon=False)
ax.add_artist(x_asb)
ax.add_artist(y_asb)
plt.draw()
plt.show()
On 21.02.2012, at 11:53, Bartosz Telenczuk wrote:
> Hi all,
>
> I am trying to add to the axes a sizebar (a line of length specified in data
> coordinates) at a fixed location relative to the axes (in axes coordinates).
> The idea is that I have several subplots with different scales and I want to
> add scalebar at the same position to each of them.
>
> I tried using ScaledTranslation transformation, but with no success (after
> export to SVG the scalebars are gone). I thought that I might use OffsetBox
> (the same that the legend is based on), but I have no idea how to use it.
>
> Do you have any suggestions?
>
> Thanks,
>
> Bartosz
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Bartosz Telenczuk
Institute for Theoretical Biology
Humboldt University of Berlin, Germany
Phone: +4930/2093-8838
Homepage: http://neuroscience.telenczuk.pl
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