"""
===========================================
Overlaying differentially rotated gridlines
===========================================

How to overlay differentially rotated gridlines on a Map.

The example uses the `~sunpy.coordinates.metaframes.RotatedSunFrame` coordinate
metaframe in `sunpy.coordinates` to overlay differentially rotated gridlines on
a Map. See :ref:`sunpy-topic-guide-coordinates-rotatedsunframe` for more details on using
`~sunpy.coordinates.metaframes.RotatedSunFrame`.
"""
import matplotlib.pyplot as plt

import astropy.units as u

import sunpy.map
from sunpy.coordinates import HeliographicStonyhurst, RotatedSunFrame
from sunpy.data.sample import AIA_171_IMAGE

##############################################################################
# Let's use an AIA observation, and plot lines of constant longitude in
# heliographic Stonyhurst. We'll plot the normal lines (prior to applying
# differential rotation) in white and the differentially rotated lines in
# blue.

# sphinx_gallery_defer_figures

aiamap = sunpy.map.Map(AIA_171_IMAGE)
fig = plt.figure()
ax = fig.add_subplot(projection=aiamap)
aiamap.plot(axes=ax, clip_interval=(1., 99.95)*u.percent)

##############################################################################
# Lines of constant longitude prior to differential rotation

# sphinx_gallery_defer_figures

overlay1 = ax.get_coords_overlay('heliographic_stonyhurst')
overlay1[0].set_ticks(spacing=15. * u.deg)
overlay1[1].set_ticks(spacing=90. * u.deg)
overlay1.grid(ls='-', color='white')

##############################################################################
# Differentially rotating the lines of constant longitude by 27 days
# Be aware that the differentially rotated lines are plotted in the
# original coordinate frame, so it doesn't account for any motion of the
# observer over 27 days.

rs_hgs = RotatedSunFrame(base=HeliographicStonyhurst(obstime=aiamap.date),
                         duration=27*u.day)
overlay2 = ax.get_coords_overlay(rs_hgs)
overlay2[0].set_ticks(spacing=15. * u.deg)
overlay2[1].set_ticks(spacing=90. * u.deg)
overlay2.grid(ls='-', color='blue')

plt.show()