Plotting Glyphs (Vectors or PolyData)

Use vectors in a dataset to plot and orient glyphs/geometric objects.

# sphinx_gallery_thumbnail_number = 4
import pyvista as pv
from pyvista import examples
import numpy as np

Glyphying can be done via the pyvista.DataSetFilters.glyph() filter

mesh = examples.download_carotid().threshold(145, scalars="scalars")
mask = mesh['scalars'] < 210
mesh['scalars'][mask] = 0  # null out smaller vectors

# Make a geometric object to use as the glyph
geom = pv.Arrow()  # This could be any dataset

# Perform the glyph
glyphs = mesh.glyph(orient="vectors", scale="scalars", factor=0.003, geom=geom)

# plot using the plotting class
pl = pv.Plotter()
pl.add_mesh(glyphs, show_scalar_bar=False, lighting=False, cmap='coolwarm')
pl.camera_position = [(146.53, 91.28, 21.70),
                      (125.00, 94.45, 19.81),
                      (-0.086, 0.007, 0.996)]  # view only part of the vector field
cpos = pl.show(return_cpos=True)

Another approach is to load the vectors directly to the mesh object and then access the pyvista.DataSet.arrows property.

sphere = pv.Sphere(radius=3.14)

# make cool swirly pattern
vectors = np.vstack(
    (
        np.sin(sphere.points[:, 0]),
        np.cos(sphere.points[:, 1]),
        np.cos(sphere.points[:, 2]),
    )
).T

# add and scale
sphere["vectors"] = vectors * 0.3
sphere.set_active_vectors("vectors")

# plot just the arrows
sphere.arrows.plot()

Plot the arrows and the sphere.

p = pv.Plotter()
p.add_mesh(sphere.arrows, lighting=False,
           scalar_bar_args={'title': "Vector Magnitude"})
p.add_mesh(sphere, color="grey", ambient=0.6, opacity=0.5, show_edges=False)
p.show()

Subset of Glyphs

Sometimes you might not want glyphs for every node in the input dataset. In this case, you can choose to build glyphs for a subset of the input dataset by using a merging tolerance. Here we specify a merging tolerance of five percent which equates to five percent of the bounding box’s length.

# Example dataset with normals
mesh = examples.load_random_hills()

# create a subset of arrows using the glyph filter
arrows = mesh.glyph(scale="Normals", orient="Normals", tolerance=0.05)

p = pv.Plotter()
p.add_mesh(arrows, color="black")
p.add_mesh(mesh, scalars="Elevation", cmap="terrain", smooth_shading=True)
p.show()