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DOC: Simplify Line, Poly and RegularPoly example #30383

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Aug 3, 2025
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DOC: Simplify Line, Poly and RegularPoly example #30383

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44 changes: 12 additions & 32 deletions galleries/examples/shapes_and_collections/collections.py
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Original file line number Diff line number Diff line change
Expand Up @@ -47,53 +47,36 @@


col = collections.LineCollection(
[spiral], offsets=xyo, offset_transform=ax1.transData)
[spiral], offsets=xyo, offset_transform=ax1.transData, color=colors)
# transform the line segments such that their size is given in points
trans = fig.dpi_scale_trans + transforms.Affine2D().scale(1.0/72.0)
col.set_transform(trans) # the points to pixels transform
# Note: the first argument to the collection initializer
# must be a list of sequences of (x, y) tuples; we have only
# one sequence, but we still have to put it in a list.
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This note is out of place it refers to LineCollection([spiral], ..., but I claim this is enough of a standard pattern that we don't need to mention it.

ax1.add_collection(col, autolim=True)
# autolim=True enables autoscaling. For collections with
# offsets like this, it is neither efficient nor accurate,
# but it is good enough to generate a plot that you can use
# as a starting point. If you know beforehand the range of
# x and y that you want to show, it is better to set them
# explicitly, set the *autolim* keyword argument to False.
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This is unclear: Why is it neither efficient nor accurate. I'm also not clear whether the statement is still correct. It's from 2006 and collection limit handling as improved since then. If anything we'd need an explicit discussion on limit handling for collections, but that's not the scope of this example. So let's remove this here.


# Make a transform for the line segments such that their size is
# given in points:
col.set_color(colors)

ax1.add_collection(col)
ax1.set_title('LineCollection using offsets')


# The same data as above, but fill the curves.
col = collections.PolyCollection(
[spiral], offsets=xyo, offset_transform=ax2.transData)
[spiral], offsets=xyo, offset_transform=ax2.transData, color=colors)
trans = transforms.Affine2D().scale(fig.dpi/72.0)
col.set_transform(trans) # the points to pixels transform
ax2.add_collection(col, autolim=True)
col.set_color(colors)


ax2.add_collection(col)
ax2.set_title('PolyCollection using offsets')

# 7-sided regular polygons

# 7-sided regular polygons
col = collections.RegularPolyCollection(
7, sizes=np.abs(xx) * 10.0, offsets=xyo, offset_transform=ax3.transData)
7, sizes=np.abs(xx) * 10.0, offsets=xyo, offset_transform=ax3.transData,
color=colors)
trans = transforms.Affine2D().scale(fig.dpi / 72.0)
col.set_transform(trans) # the points to pixels transform
ax3.add_collection(col, autolim=True)
col.set_color(colors)
ax3.add_collection(col)
ax3.set_title('RegularPolyCollection using offsets')


# Simulate a series of ocean current profiles, successively
# offset by 0.1 m/s so that they form what is sometimes called
# a "waterfall" plot or a "stagger" plot.

nverts = 60
ncurves = 20
offs = (0.1, 0.0)
Expand All @@ -107,15 +90,12 @@
curve = np.column_stack([xxx, yy * 100])
segs.append(curve)

col = collections.LineCollection(segs, offsets=offs)
ax4.add_collection(col, autolim=True)
col.set_color(colors)
col = collections.LineCollection(segs, offsets=offs, color=colors)
ax4.add_collection(col)
ax4.set_title('Successive data offsets')
ax4.set_xlabel('Zonal velocity component (m/s)')
ax4.set_ylabel('Depth (m)')
# Reverse the y-axis so depth increases downward
ax4.set_ylim(ax4.get_ylim()[::-1])

ax4.invert_yaxis() # so that depth increases downward

plt.show()

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