I’ve worked out how to create a Poly3DCollection as noted by Maximilian Albert
and how to use the set_array method on the collection created by plot_trisurf
as noted by Geoffroy Billotey. I have two follow up questions:
1) Would it be possible to make it so that if the color parameter of
plot_trisurf is an array of length n_triangles, that plot_trisurf would
internally use set_array to color the triangles with the colors in the color
parameter?
2) Is there a way to color the triangles with gradients? I have an
intensity value at each vertex of the triangles so Matlab/octave colors each
triangle with a gradient whereas right now I’m taking an average of the values
at the vertices and assigning the resulting value to the triangle.
Byron Boulton
From: Geoffroy Billotey [mailto:geoffroy.billo...@gmail.com]
Sent: Wednesday, January 21, 2015 12:33 PM
To: matplotlib-devel@lists.sourceforge.net; Byron K. Boulton
Subject: Re: [matplotlib-devel] trisurf plots with independent color data
Hi,
You can also try to pass a *color* array of size ntri (number of triangles) to
the *set_array* method of the collection returned by *plot_trisurf*.
See for instance:
http://stackoverflow.com/questions/24218543/colouring-the-surface-of-a-sphere-with-a-set-of-scalar-values-in-matplotlib/24229480#24229480<http://cp.mcafee.com/d/1jWVIq40USyMCyYUy-qenztPqdQPhOCepshhdETjd7aoVBNOVJ6WpEVj7cK8FCQrFCzBcsOUeKr85i5mPVRw2y7NzbOszP-ndAfz6nAV7DYKrggjZQwM_R-puK-_RXBQSkSu7fcEKsJteOaqJTCel3PWApmU6CQjrVK_9IInojvvpjdTdw0WjSNmFDUKDRcsLwITZ9OH2C9I9ELfIcVqFZmUOwhbP9-nET5TrunGWnQLhoDYvbC9j9BZbQ-puHFuBJfS9sPFXvQbOwnlSqNZpDO8oCMCCqem7HwoCMCCqem7HCOfRttzkJN2hVZp-m1h4jVsSyMMCMr1vF6y0QJGXdo-IPV42W7CvfdbFEwD6l6UKCy1o-IW6y0NapcQgiwxWTMg-4Ph1qFZoCy13pWrsodTc9QClIZK1f8>
2015-01-21 17:02 GMT+01:00 Maximilian Albert
<maximilian.alb...@gmail.com<mailto:maximilian.alb...@gmail.com>>:
Hi Byron,
This is a bit of a workaround, but you can specify facecolors explicitly by
creating a triangulation of your surface explicitly and creating a
Poly3DCollection with these facecolors. I'm attaching an example below which is
a modified version of the plot_trisurf demo [1] in the matplotlib
documentation. It showcases both random colors and a smooth gradient (the
latter in the line that's commented out).
I would have thought that it should be possible to pass an argument like
"facecolors" to plot_trisurf directly, since the documentation [2] states that
"other arguments are passed on to Poly3DCollection". However, I couldn't get
this to work quickly. Maybe someone else knows how?
Best regards,
Max
[1]
http://matplotlib.org/examples/mplot3d/trisurf3d_demo.html<http://cp.mcafee.com/d/k-Kr6x0SyMCyYUy-qenztPqdQPhOCepshhdETjd7aoVBNOVJ6WpEVj7cK8FCQrFCzBcsOUeKr85i5mPVRw2y7NzbOszP-ndAfz6nAV7DYKrggjZQwM_R-puK-_RXBQSkSu7fcEKsJteOaqJTCel3PWApmU6CQPrVK_9IInojvvpjdTdw0RtCIvmpYy700sYf21_QNlo-ISkcD6l6UKIE2G7GRU76OfRttzkJN2hVZp-m1h4jVsSyMMCMr1vF6y0QJGXdo-IPV42W7CvfdbFEwD6l6UKCy1o-IW6y0NapcQgiwxWTMg-4Ph1qFZoCy13pWrsodCuBsX5L->
[2]
http://matplotlib.org/mpl_toolkits/mplot3d/api.html<http://cp.mcafee.com/d/1jWVIq6h8gdEI9ELe8LCzBUTsSztcQsFzCn4kjqdQPhOCepssKrhKCqekNPbyapJ6WpEVj7cK3HCO1kxlI-to0ExYoOYD8Y_BPp3UNBVehV_bCQ44_t8cfZvCnHLLZuVtdBdDxPPabDbnjIyCHtVzBgY-F6lK1FJAS-rLOrb5S4TTSkPtPo0dnpH7RCv8xM075lzNmtqDBpjFyGNZpIEpGQK1NIzZnnoRbsgAuvmvBwkh4-ndEIc9I6MnWhEwdbqKPmfHc-h0KxVDPPiWq89NBhKbFEwmfHexEwciCjd44E8uJY4fxcQgmGvm9EwgSuCT63oeMA92eD>
from mpl_toolkits.mplot3d import Axes3D
from matplotlib import cm
import matplotlib.pyplot as plt
import numpy as np
from matplotlib.tri import Triangulation
from mpl_toolkits.mplot3d.art3d import Poly3DCollection
n_angles = 36
n_radii = 8
# An array of radii
# Does not include radius r=0, this is to eliminate duplicate points
radii = np.linspace(0.125, 1.0, n_radii)
# An array of angles
angles = np.linspace(0, 2*np.pi, n_angles, endpoint=False)
# Repeat all angles for each radius
angles = np.repeat(angles[...,np.newaxis], n_radii, axis=1)
# Convert polar (radii, angles) coords to cartesian (x, y) coords
# (0, 0) is added here. There are no duplicate points in the (x, y) plane
x = np.append(0, (radii*np.cos(angles)).flatten())
y = np.append(0, (radii*np.sin(angles)).flatten())
# Pringle surface
z = np.sin(-x*y)
tri = Triangulation(x, y) # NOTE: This assumes that there is a nice projection
of the surface into the x/y-plane!
triangle_vertices = np.array([np.array([[x[T[0]], y[T[0]], z[T[0]]],
[x[T[1]], y[T[1]], z[T[1]]],
[x[T[2]], y[T[2]], z[T[2]]]]) for T in
tri.triangles])
midpoints = np.average(triangle_vertices, axis=1)
def find_color_for_point(pt):
x, y, z = pt
col = [(y+1)/2, (1-y)/2, 0]
return col
#facecolors = [find_color_for_point(pt) for pt in midpoints] # smooth gradient
facecolors = [np.random.random(3) for pt in midpoints] # random colors
coll = Poly3DCollection(triangle_vertices, facecolors=facecolors,
edgecolors='black')
fig = plt.figure()
ax = fig.gca(projection='3d')
ax.add_collection(coll)
ax.set_xlim(-1, 1)
ax.set_ylim(-1, 1)
ax.set_zlim(-1, 1)
ax.elev = 50
plt.show()
------------------------------------------------------------------------------
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