"""
===================================
AIA to STEREO coordinate conversion
===================================

How to convert a point of a source on an AIA image
to a position on a STEREO image.
"""
# sphinx_gallery_thumbnail_number = 5

import matplotlib.pyplot as plt

import astropy.units as u
from astropy.coordinates import SkyCoord

import sunpy.coordinates
import sunpy.map
from sunpy.data.sample import AIA_193_JUN2012, STEREO_A_195_JUN2012
from sunpy.sun import constants

###############################################################################
# Create a dictionary with the two maps, cropped down to full disk.

maps = {m.detector: m.submap(SkyCoord([-1100, 1100]*u.arcsec,
                                      [-1100, 1100]*u.arcsec,
                                      frame=m.coordinate_frame))
        for m in sunpy.map.Map([AIA_193_JUN2012, STEREO_A_195_JUN2012])}
maps['AIA'].plot_settings['vmin'] = 0  # set the minimum plotted pixel value


###############################################################################
# We will be transforming coordinates where the formation height of 304 A
# emission makes a difference, so we set the reference solar radius to 4 Mm
# above the solar surface (see `Alissandrakis 2019
# <https://doi.org/10.1007/s11207-019-1552-1>`__).

for m in maps.values():
    m.meta['rsun_ref'] = (constants.radius + 4*u.Mm).to_value('m')

###############################################################################
# Plot both maps.

fig = plt.figure(figsize=(10, 4))
for i, m in enumerate(maps.values()):
    ax = fig.add_subplot(1, 2, i+1, projection=m)
    m.plot(axes=ax)

###############################################################################
# We are now going to pick out a region around the south west corner:

aia_bottom_left = SkyCoord(700 * u.arcsec,
                           100 * u.arcsec,
                           frame=maps['AIA'].coordinate_frame)
aia_top_right = SkyCoord(850 * u.arcsec,
                         350 * u.arcsec,
                         frame=maps['AIA'].coordinate_frame)

###############################################################################
# Plot a rectangle around the region we want to crop.

fig = plt.figure()
ax = fig.add_subplot(projection=maps['AIA'])
maps['AIA'].plot(axes=ax)
maps['AIA'].draw_quadrangle(aia_bottom_left, top_right=aia_top_right)

###############################################################################
# Create a submap of this area and draw an X at a specific feature of interest.

subaia = maps['AIA'].submap(aia_bottom_left, top_right=aia_top_right)
fig = plt.figure()
ax = fig.add_subplot(projection=subaia)
subaia.plot(axes=ax)

feature_aia = SkyCoord(800 * u.arcsec,
                       300 * u.arcsec,
                       frame=maps['AIA'].coordinate_frame)
ax.plot_coord(feature_aia, 'bx', fillstyle='none', markersize=20)

###############################################################################
# We can transform the coordinate of the feature to see its representation as
# seen by STEREO EUVI.  The original coordinate did not contain a distance from
# the observer, so it is converted to a 3D coordinate assuming that it has a
# radius from Sun center equal to the reference solar radius of the coordinate
# frame, which we set earlier to be the formation height of 304 A emission.

print(feature_aia.transform_to(maps['EUVI'].coordinate_frame))

###############################################################################
# Now we can plot this box on both the AIA and EUVI images.  Note that using
# :meth:`~sunpy.map.GenericMap.draw_quadrangle` means that the plotted
# rectangle will be automatically warped appropriately to account for the
# different coordinate frames.

fig = plt.figure(figsize=(10, 4))

ax1 = fig.add_subplot(121, projection=maps['AIA'])
maps['AIA'].plot(axes=ax1)
maps['AIA'].draw_quadrangle(aia_bottom_left, top_right=aia_top_right, axes=ax1)

ax2 = fig.add_subplot(122, projection=maps['EUVI'])
maps['EUVI'].plot(axes=ax2)
maps['AIA'].draw_quadrangle(aia_bottom_left, top_right=aia_top_right, axes=ax2)

###############################################################################
# We can now zoom in on the region in the EUVI image, and we also draw an X
# at the feature marked earlier.  We do not need to explicitly transform the
# feature coordinate to the matching coordinate frame; that is performed
# automatically by :meth:`~astropy.visualization.wcsaxes.WCSAxes.plot_coord`.

fig = plt.figure(figsize=(15, 5))

ax1 = fig.add_subplot(121, projection=subaia)
subaia.plot(axes=ax1)
ax1.plot_coord(feature_aia, 'bx', fillstyle='none', markersize=20)

subeuvi = maps['EUVI'].submap(aia_bottom_left, top_right=aia_top_right)

ax2 = fig.add_subplot(122, projection=subeuvi)
subeuvi.plot(axes=ax2)
maps['AIA'].draw_quadrangle(aia_bottom_left, top_right=aia_top_right, axes=ax2)
ax2.plot_coord(feature_aia, 'bx', fillstyle='none', markersize=20)

plt.show()