Add vectors color by angle

This example generates a set of vectors in a spiral pattern. The color of the vectors is mapped to their ‘angle’ feature.

Tags: visualization-advanced

import napari
from skimage import data
import numpy as np


# create the viewer and window
viewer = napari.Viewer()

layer = viewer.add_image(data.camera(), name='photographer')

# sample vector coord-like data
n = 300
pos = np.zeros((n, 2, 2), dtype=np.float32)
phi_space = np.linspace(0, 4 * np.pi, n)
radius_space = np.linspace(0, 100, n)

# assign x-y position
pos[:, 0, 0] = radius_space * np.cos(phi_space) + 300
pos[:, 0, 1] = radius_space * np.sin(phi_space) + 256

# assign x-y projection
pos[:, 1, 0] = 2 * radius_space * np.cos(phi_space)
pos[:, 1, 1] = 2 * radius_space * np.sin(phi_space)

# make the angle feature, range 0-2pi
angle = np.mod(phi_space, 2 * np.pi)

# create a feature that is true for all angles  > pi
pos_angle = angle > np.pi

# create the features dictionary.
features = {
    'angle': angle,
    'pos_angle': pos_angle,
}

# add the vectors
layer = viewer.add_vectors(
    pos,
    edge_width=3,
    features=features,
    edge_color='angle',
    edge_colormap='husl',
    name='vectors'
)

# set the edge color mode to colormap
layer.edge_color_mode = 'colormap'

if __name__ == '__main__':
    napari.run()

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