Created
July 6, 2010 08:14
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from math import sqrt | |
from matplotlib import pyplot | |
from shapely.geometry import * | |
GM = (sqrt(5)-1.0)/2.0 | |
W = 8.0 | |
H = W*GM | |
SIZE = (W, H) | |
COLORS = ['#6699cc', '#ffcc33'] | |
def cut(line, distance): | |
# Cuts a line in two at a distance from its starting point | |
if distance <= 0.0 or distance >= line.length: | |
return [LineString(line)] | |
coords = list(line.coords) | |
for i, p in enumerate(coords): | |
pd = line.project(Point(p)) | |
if pd == distance: | |
return [ | |
LineString(coords[:i+1]), | |
LineString(coords[i:])] | |
if pd > distance: | |
cp = line.interpolate(distance) | |
return [ | |
LineString(coords[:i] + [(cp.x, cp.y)]), | |
LineString([(cp.x, cp.y)] + coords[i:])] | |
def plot_coords(ax, ob): | |
# Plot a line's coordinates | |
x, y = ob.xy | |
ax.plot(x, y, 'o', color='#999999', zorder=1) | |
def plot_bounds(ax, ob): | |
# Plot a line's boundary | |
x, y = zip(*list((p.x, p.y) for p in ob.boundary)) | |
ax.plot(x, y, 'o', color='#000000', zorder=1) | |
def plot_line(ax, ob, color='#999999'): | |
# Plot a line | |
x, y = ob.xy | |
ax.plot(x, y, color=color, alpha=0.7, linewidth=3, solid_capstyle='round', zorder=2) | |
def arrange(axes): | |
# Set axes parameters | |
xrange = [-1, 4] | |
yrange = [-1, 3] | |
axes.set_xlim(*xrange) | |
axes.set_ylim(*yrange) | |
axes.set_yticks(range(*yrange) + [yrange[-1]]) | |
axes.set_aspect(1) | |
# The figure | |
fig = pyplot.figure(1, figsize=SIZE, dpi=90) | |
# A simple (non-crossing) line | |
line = LineString([(0, 0), (1, 1), (0, 2), (2, 2), (3, 1), (1, 0)]) | |
# 1: plot the line | |
ax = fig.add_subplot(121) | |
plot_coords(ax, line) | |
plot_bounds(ax, line) | |
plot_line(ax, line) | |
arrange(ax) | |
ax.set_title('a) Before') | |
# 2: cut the line and plot the pieces | |
ax = fig.add_subplot(122) | |
for piece, color in zip(cut(line, line.length/2.0), COLORS): | |
plot_coords(ax, piece) | |
plot_bounds(ax, piece) | |
plot_line(ax, piece, color=color) | |
arrange(ax) | |
ax.set_title('b) After') | |
pyplot.show() | |
# pyplot.savefig('cut.png') |
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cut function fails when the line contains the same point multiple times. Using the cumulative distance between each point solved this: