Plotting wind vectors (wind speed and direction)

gistfile1.py

import numpy as np

import matplotlib.pyplot as plt

import cartopy.crs as ccrs
import iris
from iris.coord_systems import GeogCS
from iris.cube import Cube


def create_random_wind_data(size):
    # Create some random wind data
    def random_dat(size):
        return (np.random.random_sample(size)*2-1)*10

    # Coord system
    cs = GeogCS(6371229)

    # Coordinates
    lat_coord = iris.coords.DimCoord(
        points=np.linspace(45, 60, size[0], endpoint=True),
        standard_name='latitude',
        units='degrees',
        coord_system=cs)

    lon_coord = iris.coords.DimCoord(
        points=np.linspace(-10, 5, size[1], endpoint=True),
        standard_name='longitude',
        units='degrees',
        coord_system=cs)

    # U-wind cube
    u_cube = Cube(random_dat(size),
                  standard_name='eastward_wind',
                  units='m s-1')

    u_cube.add_dim_coord(lat_coord, 0)
    u_cube.add_dim_coord(lon_coord, 1)

    # V-wind cube
    v_cube = Cube(random_dat(size),
                  standard_name='northward_wind',
                  units='m s-1')

    v_cube.add_dim_coord(lat_coord, 0)
    v_cube.add_dim_coord(lon_coord, 1)

    return (u_cube, v_cube)


if __name__ == '__main__':
    u_cube, v_cube = create_random_wind_data(size=(25, 25))

    # Quiver plot
    U = u_cube.data
    V = v_cube.data
    X = u_cube.coord('longitude').points
    Y = v_cube.coord('latitude').points

    ax = plt.axes(projection=ccrs.PlateCarree())
    arrows = plt.quiver(X, Y, U, V, units='xy', headwidth=2,
                        transform=ccrs.Geodetic())
    ax.coastlines()
    ax.gridlines(draw_labels=True)
    ax.stock_img()
    ax.set_xlim(-10, 5)
    ax.set_ylim(45, 60)

    plt.show()

Thanks for sharing this!

When I run this I get the following error. Any idea why?! When I comment out the transform=ccrs.Geodetic() bit, it works fine. Thanks!...

---

ValueError Traceback (most recent call last)
in ()
----> 1 execfile('global_4deg.py')

/scale_akl_persistent/filesets/home/williamsjh/veros-analysis/global_4deg.py in ()
80 ax = plt.axes(projection=ccrs.PlateCarree())
81 arrows = plt.quiver(X, Y, U, V, units='xy', headwidth=2,
---> 82 transform=ccrs.Geodetic())
83 ax.coastlines()
84 ax.gridlines(draw_labels=True)

/home/williamsjh/.conda/envs/my_root/lib/python2.7/site-packages/matplotlib/pyplot.pyc in quiver(*args, **kw)
3210 ax.hold(hold)
3211 try:
-> 3212 ret = ax.quiver(*args, **kw)
3213 finally:
3214 ax.hold(washold)

/home/williamsjh/.conda/envs/my_root/lib/python2.7/site-packages/cartopy/mpl/geoaxes.pyc in quiver(self, x, y, u, v, *args, **kwargs)
1678 t = self.projection
1679 if isinstance(t, ccrs.CRS) and not isinstance(t, ccrs.Projection):
-> 1680 raise ValueError('invalid transform:'
1681 ' Spherical quiver is not supported - '
1682 ' consider using PlateCarree/RotatedPole.')

ValueError: invalid transform: Spherical quiver is not supported - consider using PlateCarree/RotatedPole.

In [57]: