"""
========================================================
Demonstration of advanced quiver and quiverkey functions
========================================================

Demonstrates some more advanced options for `~.axes.Axes.quiver`.  For a simple
example refer to :doc:`/gallery/images_contours_and_fields/quiver_simple_demo`.

Known problem: the plot autoscaling does not take into account the arrows, so
those on the boundaries are often out of the picture.  This is *not* an easy
problem to solve in a perfectly general way.  The workaround is to manually
expand the Axes objects.
"""
import matplotlib.pyplot as plt
import numpy as np
from numpy import ma

X, Y = np.meshgrid(np.arange(0, 2 * np.pi, .2), np.arange(0, 2 * np.pi, .2))
U = np.cos(X)
V = np.sin(Y)

###############################################################################

fig1, ax1 = plt.subplots()
ax1.set_title('Arrows scale with plot width, not view')
Q = ax1.quiver(X, Y, U, V, units='width')
qk = ax1.quiverkey(Q, 0.9, 0.9, 2, r'$2 \frac{m}{s}$', labelpos='E',
                   coordinates='figure')

###############################################################################

fig2, ax2 = plt.subplots()
ax2.set_title("pivot='mid'; every third arrow; units='inches'")
Q = ax2.quiver(X[::3, ::3], Y[::3, ::3], U[::3, ::3], V[::3, ::3],
               pivot='mid', units='inches')
qk = ax2.quiverkey(Q, 0.9, 0.9, 1, r'$1 \frac{m}{s}$', labelpos='E',
                   coordinates='figure')
ax2.scatter(X[::3, ::3], Y[::3, ::3], color='r', s=5)

###############################################################################

fig3, ax3 = plt.subplots()
ax3.set_title("pivot='tip'; scales with x view")
M = np.hypot(U, V)
Q = ax3.quiver(X, Y, U, V, M, units='x', pivot='tip', width=0.022,
               scale=1 / 0.15)
qk = ax3.quiverkey(Q, 0.9, 0.9, 1, r'$1 \frac{m}{s}$', labelpos='E',
                   coordinates='figure')
ax3.scatter(X, Y, color='k', s=5)

plt.show()

#############################################################################
#
# ------------
#
# References
# """"""""""
#
# The use of the following functions and methods is shown in this example:

import matplotlib
matplotlib.axes.Axes.quiver
matplotlib.pyplot.quiver
matplotlib.axes.Axes.quiverkey
matplotlib.pyplot.quiverkey
