'''
Demonstration of wind barb plots
'''
import matplotlib.pyplot as plt
import numpy as np

def main():
    x = np.linspace(-5, 5, 5)
    X, Y = np.meshgrid(x, x)
    U, V = 12*X, 12*Y

    data = [(-1.5, .5, -6, -6),
            (1, -1, -46, 46),
            (-3, -1, 11, -11),
            (1, 1.5, 80, 80),
            (0.5, 0.25, 25, 15),
            (-1.5, -0.5, -5, 40)]

    data = np.array(data, dtype=[('x', np.float32), ('y', np.float32),
                                 ('u', np.float32), ('v', np.float32)])

    # Default parameters, uniform grid
    ax = plt.subplot(2, 2, 1)
    ax.barbs(X, Y, U, V)

    # Arbitrary set of vectors, make them longer and change the pivot point
    #(point around which they're rotated) to be the middle
    ax = plt.subplot(2, 2, 2)
    ax.barbs(data['x'], data['y'], data['u'], data['v'], length=8, pivot='middle')

    # Showing colormapping with uniform grid.  Fill the circle for an empty barb,
    # don't round the values, and change some of the size parameters
    ax = plt.subplot(2, 2, 3)
    ax.barbs(X, Y, U, V, np.sqrt(U*U + V*V), fill_empty=True, rounding=False,
             sizes=dict(emptybarb=0.25, spacing=0.2, height=0.3))

    # Change colors as well as the increments for parts of the barbs
    ax = plt.subplot(2, 2, 4)
    ax.barbs(data['x'], data['y'], data['u'], data['v'], flagcolor='r',
             barbcolor=['b', 'g'], barb_increments=dict(half=10, full=20, flag=100),
             flip_barb=True)

    # Masked arrays are also supported
    masked_u = np.ma.masked_array(data['u'])
    masked_u[4] = 1000  # Bad value that should not be plotted when masked
    masked_u[4] = np.ma.masked

    # Identical plot to panel 2 in the first figure, but with the point at
    #(0.5, 0.25) missing (masked)
    fig2 = plt.figure()
    ax = fig2.add_subplot(1, 1, 1)
    poly_collection = ax.barbs(data['x'], data['y'], masked_u, data['v'], length=8, pivot='middle')

    plt.savefig("barb")
    return poly_collection

if __name__ == '__main__':
    main()
