Note

Click here to download the full example code

09. Triangular grids with mpl.tripcolor

This script demonstrates how to visualize data on an unstructured triangular grid using matplotlib.tripcolor. This is useful for plotting data that is not arranged in a regular grid.

The example covers two main scenarios:

  • Automatically creating a Delaunay triangulation from a set of 2D points.

  • Plotting data on a pre-defined, user-specified mesh of triangles.

  • It also compares flat and gouraud shading methods.

  • tripcolor of Delaunay triangulation, flat shading
  • tripcolor of Delaunay triangulation, gouraud shading
  • tripcolor of user-specified triangulation

Out:

C:\Users\kelda\Desktop\repositories\github\python-spare-code\main\examples\matplotlib\plot_main09_tripcolor.py:112: UserWarning:

FigureCanvasAgg is non-interactive, and thus cannot be shown


 18 import matplotlib.pyplot as plt
 19 import matplotlib.tri as tri
 20 import numpy as np
 21
 22 # First create the x and y coordinates of the points.
 23 n_angles = 36
 24 n_radii = 8
 25 min_radius = 0.25
 26 radii = np.linspace(min_radius, 0.95, n_radii)
 27
 28 angles = np.linspace(0, 2 * np.pi, n_angles, endpoint=False)
 29 angles = np.repeat(angles[..., np.newaxis], n_radii, axis=1)
 30 angles[:, 1::2] += np.pi / n_angles
 31
 32 x = (radii * np.cos(angles)).flatten()
 33 y = (radii * np.sin(angles)).flatten()
 34 z = (np.cos(radii) * np.cos(3 * angles)).flatten()
 35
 36 # Create the Triangulation; no triangles so Delaunay triangulation created.
 37 triang = tri.Triangulation(x, y)
 38
 39 # Mask off unwanted triangles.
 40 triang.set_mask(np.hypot(x[triang.triangles].mean(axis=1),
 41                          y[triang.triangles].mean(axis=1))
 42                 < min_radius)
 43
 44 fig1, ax1 = plt.subplots()
 45 ax1.set_aspect('equal')
 46 tpc = ax1.tripcolor(triang, z, shading='flat')
 47 fig1.colorbar(tpc)
 48 ax1.set_title('tripcolor of Delaunay triangulation, flat shading')
 49
 50 fig2, ax2 = plt.subplots()
 51 ax2.set_aspect('equal')
 52 tpc = ax2.tripcolor(triang, z, shading='gouraud')
 53 fig2.colorbar(tpc)
 54 ax2.set_title('tripcolor of Delaunay triangulation, gouraud shading')
 55
 56
 57 xy = np.asarray([
 58     [-0.101, 0.872], [-0.080, 0.883], [-0.069, 0.888], [-0.054, 0.890],
 59     [-0.045, 0.897], [-0.057, 0.895], [-0.073, 0.900], [-0.087, 0.898],
 60     [-0.090, 0.904], [-0.069, 0.907], [-0.069, 0.921], [-0.080, 0.919],
 61     [-0.073, 0.928], [-0.052, 0.930], [-0.048, 0.942], [-0.062, 0.949],
 62     [-0.054, 0.958], [-0.069, 0.954], [-0.087, 0.952], [-0.087, 0.959],
 63     [-0.080, 0.966], [-0.085, 0.973], [-0.087, 0.965], [-0.097, 0.965],
 64     [-0.097, 0.975], [-0.092, 0.984], [-0.101, 0.980], [-0.108, 0.980],
 65     [-0.104, 0.987], [-0.102, 0.993], [-0.115, 1.001], [-0.099, 0.996],
 66     [-0.101, 1.007], [-0.090, 1.010], [-0.087, 1.021], [-0.069, 1.021],
 67     [-0.052, 1.022], [-0.052, 1.017], [-0.069, 1.010], [-0.064, 1.005],
 68     [-0.048, 1.005], [-0.031, 1.005], [-0.031, 0.996], [-0.040, 0.987],
 69     [-0.045, 0.980], [-0.052, 0.975], [-0.040, 0.973], [-0.026, 0.968],
 70     [-0.020, 0.954], [-0.006, 0.947], [ 0.003, 0.935], [ 0.006, 0.926],
 71     [ 0.005, 0.921], [ 0.022, 0.923], [ 0.033, 0.912], [ 0.029, 0.905],
 72     [ 0.017, 0.900], [ 0.012, 0.895], [ 0.027, 0.893], [ 0.019, 0.886],
 73     [ 0.001, 0.883], [-0.012, 0.884], [-0.029, 0.883], [-0.038, 0.879],
 74     [-0.057, 0.881], [-0.062, 0.876], [-0.078, 0.876], [-0.087, 0.872],
 75     [-0.030, 0.907], [-0.007, 0.905], [-0.057, 0.916], [-0.025, 0.933],
 76     [-0.077, 0.990], [-0.059, 0.993]])
 77 x, y = np.rad2deg(xy).T
 78
 79 triangles = np.asarray([
 80     [67, 66,  1], [65,  2, 66], [ 1, 66,  2], [64,  2, 65], [63,  3, 64],
 81     [60, 59, 57], [ 2, 64,  3], [ 3, 63,  4], [ 0, 67,  1], [62,  4, 63],
 82     [57, 59, 56], [59, 58, 56], [61, 60, 69], [57, 69, 60], [ 4, 62, 68],
 83     [ 6,  5,  9], [61, 68, 62], [69, 68, 61], [ 9,  5, 70], [ 6,  8,  7],
 84     [ 4, 70,  5], [ 8,  6,  9], [56, 69, 57], [69, 56, 52], [70, 10,  9],
 85     [54, 53, 55], [56, 55, 53], [68, 70,  4], [52, 56, 53], [11, 10, 12],
 86     [69, 71, 68], [68, 13, 70], [10, 70, 13], [51, 50, 52], [13, 68, 71],
 87     [52, 71, 69], [12, 10, 13], [71, 52, 50], [71, 14, 13], [50, 49, 71],
 88     [49, 48, 71], [14, 16, 15], [14, 71, 48], [17, 19, 18], [17, 20, 19],
 89     [48, 16, 14], [48, 47, 16], [47, 46, 16], [16, 46, 45], [23, 22, 24],
 90     [21, 24, 22], [17, 16, 45], [20, 17, 45], [21, 25, 24], [27, 26, 28],
 91     [20, 72, 21], [25, 21, 72], [45, 72, 20], [25, 28, 26], [44, 73, 45],
 92     [72, 45, 73], [28, 25, 29], [29, 25, 31], [43, 73, 44], [73, 43, 40],
 93     [72, 73, 39], [72, 31, 25], [42, 40, 43], [31, 30, 29], [39, 73, 40],
 94     [42, 41, 40], [72, 33, 31], [32, 31, 33], [39, 38, 72], [33, 72, 38],
 95     [33, 38, 34], [37, 35, 38], [34, 38, 35], [35, 37, 36]])
 96
 97 xmid = x[triangles].mean(axis=1)
 98 ymid = y[triangles].mean(axis=1)
 99 x0 = -5
100 y0 = 52
101 zfaces = np.exp(-0.01 * ((xmid - x0) * (xmid - x0) +
102                          (ymid - y0) * (ymid - y0)))
103
104 fig3, ax3 = plt.subplots()
105 ax3.set_aspect('equal')
106 tpc = ax3.tripcolor(x, y, triangles, facecolors=zfaces, edgecolors='k')
107 fig3.colorbar(tpc)
108 ax3.set_title('tripcolor of user-specified triangulation')
109 ax3.set_xlabel('Longitude (degrees)')
110 ax3.set_ylabel('Latitude (degrees)')
111
112 plt.show()

Total running time of the script: ( 0 minutes 0.284 seconds)

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