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MAINT: Use vectorization in plot_trisurf, simplifying greatly #9991

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Merged
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Feb 3, 2018
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MAINT: Use vectorization in plot_trisurf, simplifying greatly #9991

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43 changes: 13 additions & 30 deletions lib/mpl_toolkits/mplot3d/axes3d.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1984,47 +1984,30 @@ def plot_trisurf(self, *args, **kwargs):
args = args[1:]

triangles = tri.get_masked_triangles()
xt = tri.x[triangles][..., np.newaxis]
yt = tri.y[triangles][..., np.newaxis]
zt = z[triangles][..., np.newaxis]
xt = tri.x[triangles]
yt = tri.y[triangles]
zt = z[triangles]

verts = np.concatenate((xt, yt, zt), axis=2)

# Only need these vectors to shade if there is no cmap
if cmap is None and shade:
totpts = len(verts)
v1 = np.empty((totpts, 3))
v2 = np.empty((totpts, 3))
# This indexes the vertex points
which_pt = 0

colset = []
for i in xrange(len(verts)):
avgzsum = verts[i,0,2] + verts[i,1,2] + verts[i,2,2]
colset.append(avgzsum / 3.0)

# Only need vectors to shade if no cmap
if cmap is None and shade:
v1[which_pt] = np.array(verts[i,0]) - np.array(verts[i,1])
v2[which_pt] = np.array(verts[i,1]) - np.array(verts[i,2])
which_pt += 1

if cmap is None and shade:
normals = np.cross(v1, v2)
else:
normals = []
# verts = np.stack((xt, yt, zt), axis=-1)
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Are they 1D or 2D? np.vstack or np.dstack could also be used in those cases.

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@eric-wieser eric-wieser Dec 14, 2017 •
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Yep, this was a new change since you last reviewed. Both vstack and dstack have undesirable semantics of guessing the array .ndim, so using concatenate is more precise.

This isn't the only place that np.stack is mentioned in a comment above a np.concatenate((a[..., None], ...)), so might be worth backporting to the very simple

def stack(arrays, axis):
    return np.concatenate([arr[..., np.newaxis] for arr in arrays], axis)

- (oops, not correct)

Not something I want to involve in this PR though

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You can just stick the definition in https://github.com/matplotlib/matplotlib/blob/master/lib/matplotlib/cbook/_backports.py if you change your mind.

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Oh, and to answer your question, 2D - (N, edges_in_triangle)

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We do have a cbook._backports; not sure how strong the need is for it without having done any looking.

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I reckon there're a substantial number of cases - I can put together a PR once this is merged

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Looking again, a stack_last function is all that ever seems to be needed, implemented as the above - so that wouldn't belong in _backports. Suggestions of where to put such a helper?

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cbook would be the place.
But given that we'd probably just be using stack(..., -1) "if it was available", I'd just backport stack.
Let us know if you want to do this in this PR or a separate one.

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Definitely a separate one

verts = np.concatenate((
xt[..., np.newaxis], yt[..., np.newaxis], zt[..., np.newaxis]
), axis=-1)

polyc = art3d.Poly3DCollection(verts, *args, **kwargs)

if cmap:
colset = np.array(colset)
polyc.set_array(colset)
# average over the three points of each triangle
avg_z = verts[:, :, 2].mean(axis=1)
polyc.set_array(avg_z)
if vmin is not None or vmax is not None:
polyc.set_clim(vmin, vmax)
if norm is not None:
polyc.set_norm(norm)
else:
if shade:
v1 = verts[:, 0, :] - verts[:, 1, :]
v2 = verts[:, 1, :] - verts[:, 2, :]
normals = np.cross(v1, v2)
colset = self._shade_colors(color, normals)
else:
colset = color
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Binary file added lib/mpl_toolkits/tests/baseline_images/test_mplot3d/trisurf3d_shaded.png
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19 changes: 19 additions & 0 deletions lib/mpl_toolkits/tests/test_mplot3d.py
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Original file line number Diff line number Diff line change
Expand Up @@ -216,6 +216,25 @@ def test_trisurf3d():
ax.plot_trisurf(x, y, z, cmap=cm.jet, linewidth=0.2)


@image_comparison(baseline_images=['trisurf3d_shaded'], remove_text=True,
tol=0.03, extensions=['png'])
def test_trisurf3d_shaded():
n_angles = 36
n_radii = 8
radii = np.linspace(0.125, 1.0, n_radii)
angles = np.linspace(0, 2*np.pi, n_angles, endpoint=False)
angles = np.repeat(angles[..., np.newaxis], n_radii, axis=1)
angles[:, 1::2] += np.pi/n_angles

x = np.append(0, (radii*np.cos(angles)).flatten())
y = np.append(0, (radii*np.sin(angles)).flatten())
z = np.sin(-x*y)

fig = plt.figure()
ax = fig.gca(projection='3d')
ax.plot_trisurf(x, y, z, color=[1, 0.5, 0], linewidth=0.2)


@image_comparison(baseline_images=['wireframe3d'], remove_text=True)
def test_wireframe3d():
fig = plt.figure()
Expand Down