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多色线条#
本示例展示了两种绘制颜色随第三个值变化的线条的方法。第一个示例在每个 (x, y) 点定义颜色。第二个示例在每对点之间定义颜色，因此颜色值列表的长度比 x 和 y 列表的长度少一。
点的颜色值#
import warnings
import matplotlib.pyplot as plt
import numpy as np
from matplotlib.collections import LineCollection
def colored_line(x, y, c, ax, **lc_kwargs):
"""
Plot a line with a color specified along the line by a third value.
It does this by creating a collection of line segments. Each line segment is
made up of two straight lines each connecting the current (x, y) point to the
midpoints of the lines connecting the current point with its two neighbors.
This creates a smooth line with no gaps between the line segments.
Parameters
----------
x, y : array-like
The horizontal and vertical coordinates of the data points.
c : array-like
The color values, which should be the same size as x and y.
ax : Axes
Axis object on which to plot the colored line.
**lc_kwargs
Any additional arguments to pass to matplotlib.collections.LineCollection
constructor. This should not include the array keyword argument because
that is set to the color argument. If provided, it will be overridden.
Returns
-------
matplotlib.collections.LineCollection
The generated line collection representing the colored line.
"""
if "array" in lc_kwargs:
warnings.warn('The provided "array" keyword argument will be overridden')
# Default the capstyle to butt so that the line segments smoothly line up
default_kwargs = {"capstyle": "butt"}
default_kwargs.update(lc_kwargs)
# Compute the midpoints of the line segments. Include the first and last points
# twice so we don't need any special syntax later to handle them.
x = np.asarray(x)
y = np.asarray(y)
x_midpts = np.hstack((x[0], 0.5 * (x[1:] + x[:-1]), x[-1]))
y_midpts = np.hstack((y[0], 0.5 * (y[1:] + y[:-1]), y[-1]))
# Determine the start, middle, and end coordinate pair of each line segment.
# Use the reshape to add an extra dimension so each pair of points is in its
# own list. Then concatenate them to create:
# [
# [(x1_start, y1_start), (x1_mid, y1_mid), (x1_end, y1_end)],
# [(x2_start, y2_start), (x2_mid, y2_mid), (x2_end, y2_end)],
# ...
# ]
coord_start = np.column_stack((x_midpts[:-1], y_midpts[:-1]))[:, np.newaxis, :]
coord_mid = np.column_stack((x, y))[:, np.newaxis, :]
coord_end = np.column_stack((x_midpts[1:], y_midpts[1:]))[:, np.newaxis, :]
segments = np.concatenate((coord_start, coord_mid, coord_end), axis=1)
lc = LineCollection(segments, **default_kwargs)
lc.set_array(c) # set the colors of each segment
return ax.add_collection(lc)
# -------------- Create and show plot --------------
# Some arbitrary function that gives x, y, and color values
t = np.linspace(-7.4, -0.5, 200)
x = 0.9 * np.sin(t)
y = 0.9 * np.cos(1.6 * t)
color = np.linspace(0, 2, t.size)
# Create a figure and plot the line on it
fig1, ax1 = plt.subplots()
lines = colored_line(x, y, color, ax1, linewidth=10, cmap="plasma")
fig1.colorbar(lines) # add a color legend
# Set the axis limits and tick positions
ax1.set_xlim(-1, 1)
ax1.set_ylim(-1, 1)
ax1.set_xticks((-1, 0, 1))
ax1.set_yticks((-1, 0, 1))
ax1.set_title("Color at each point")
plt.show()
当相邻点之间的距离和颜色差异不是太大时，此方法旨在提供平滑的视觉效果。以下示例不符合此标准，因此它用于说明分段和着色机制。
点之间的颜色值#
def colored_line_between_pts(x, y, c, ax, **lc_kwargs):
"""
Plot a line with a color specified between (x, y) points by a third value.
It does this by creating a collection of line segments between each pair of
neighboring points. The color of each segment is determined by the
made up of two straight lines each connecting the current (x, y) point to the
midpoints of the lines connecting the current point with its two neighbors.
This creates a smooth line with no gaps between the line segments.
Parameters
----------
x, y : array-like
The horizontal and vertical coordinates of the data points.
c : array-like
The color values, which should have a size one less than that of x and y.
ax : Axes
Axis object on which to plot the colored line.
**lc_kwargs
Any additional arguments to pass to matplotlib.collections.LineCollection
constructor. This should not include the array keyword argument because
that is set to the color argument. If provided, it will be overridden.
Returns
-------
matplotlib.collections.LineCollection
The generated line collection representing the colored line.
"""
if "array" in lc_kwargs:
warnings.warn('The provided "array" keyword argument will be overridden')
# Check color array size (LineCollection still works, but values are unused)
if len(c) != len(x) - 1:
warnings.warn(
"The c argument should have a length one less than the length of x and y. "
"If it has the same length, use the colored_line function instead."
)
# Create a set of line segments so that we can color them individually
# This creates the points as an N x 1 x 2 array so that we can stack points
# together easily to get the segments. The segments array for line collection
# needs to be (numlines) x (points per line) x 2 (for x and y)
points = np.array([x, y]).T.reshape(-1, 1, 2)
segments = np.concatenate([points[:-1], points[1:]], axis=1)
lc = LineCollection(segments, **lc_kwargs)
# Set the values used for colormapping
lc.set_array(c)
return ax.add_collection(lc)
# -------------- Create and show plot --------------
x = np.linspace(0, 3 * np.pi, 500)
y = np.sin(x)
dydx = np.cos(0.5 * (x[:-1] + x[1:])) # first derivative
fig2, ax2 = plt.subplots()
line = colored_line_between_pts(x, y, dydx, ax2, linewidth=2, cmap="viridis")
fig2.colorbar(line, ax=ax2, label="dy/dx")
ax2.set_xlim(x.min(), x.max())
ax2.set_ylim(-1.1, 1.1)
ax2.set_title("Color between points")
plt.show()
脚本总运行时间： (0 分钟 2.829 秒)