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"""
Streamplot
----------
Generating a vector-based streamplot.
"""
import matplotlib.pyplot as plt
import cartopy.crs as ccrs
def sample_data(shape=(20, 30)):
"""
Return ``(x, y, u, v, crs)`` of some vector data
computed mathematically. The returned crs will be a rotated
pole CRS, meaning that the vectors will be unevenly spaced in
regular PlateCarree space.
"""
import numpy as np
crs = ccrs.RotatedPole(pole_longitude=177.5, pole_latitude=37.5)
x = np.linspace(311.9, 391.1, shape[1])
y = np.linspace(-23.6, 24.8, shape[0])
x2d, y2d = np.meshgrid(x, y)
u = 10 * (2 * np.cos(2 * np.deg2rad(x2d) + 3 * np.deg2rad(y2d + 30)) ** 2)
v = 20 * np.cos(6 * np.deg2rad(x2d))
return x, y, u, v, crs
def main():
fig = plt.figure(figsize=(10, 5))
ax = fig.add_subplot(1, 1, 1, projection=ccrs.PlateCarree())
ax.set_extent([-90, 75, 10, 85], crs=ccrs.PlateCarree())
ax.coastlines()
x, y, u, v, vector_crs = sample_data(shape=(80, 100))
magnitude = (u ** 2 + v ** 2) ** 0.5
ax.streamplot(x, y, u, v, transform=vector_crs,
linewidth=2, density=2, color=magnitude)
plt.show()
if __name__ == '__main__':
main()
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