Wrong frame for wide fov plots

[ManonMarchand]

In all-sky plots, we draw a rectangular frame instead of an elliptical one, see MNWE:

import matplotlib.pyplot as plt
import astropy.units as u
from astropy.coordinates import SkyCoord, Angle
from mocpy import MOC, WCS

moc = MOC.from_string('2/24')

fig = plt.figure()

with WCS(
    fig,
    fov=270 * u.deg,
    center=SkyCoord(0, 0, unit="deg", frame="galactic"),
    coordsys="galactic",
    rotation=Angle(0, u.degree),
    projection="AIT",
) as wcs:
    ax = fig.add_subplot(1, 1, 1, projection=wcs)

    moc.fill(
        ax=ax,
        wcs=wcs,
        edgecolor="teal",
        facecolor="orange",
        linewidth=1.0,
        fill=True,
        alpha=0.8,
    )

ax.grid(True)

plt.tight_layout()

However this is not as trivial as enforcing Elliptical Frame, see:

from astropy.visualization.wcsaxes.frame import EllipticalFrame
import matplotlib.pyplot as plt
import astropy.units as u
from astropy.coordinates import SkyCoord, Angle
from mocpy import MOC, WCS

moc = MOC.from_string('2/24')

fig = plt.figure()

with WCS(
    fig,
    fov=270 * u.deg,
    center=SkyCoord(0, 0, unit="deg", frame="galactic"),
    coordsys="galactic",
    rotation=Angle(0, u.degree),
    projection="AIT",
) as wcs:
    ax = fig.add_subplot(1, 1, 1, projection=wcs, frame_class=EllipticalFrame)

    moc.fill(
        ax=ax,
        wcs=wcs,
        edgecolor="teal",
        facecolor="orange",
        linewidth=1.0,
        fill=True,
        alpha=0.8,
    )

ax.grid(True)

plt.tight_layout()

There is something to investigate, don't know if the bug is upstream in astropy or with us.

[ManonMarchand]

See EllipticalFrame implementation here

class EllipticalFrame(BaseFrame):
    """
    An elliptical frame.
    """

    spine_names = "chv"

    def update_spines(self):
        xmin, xmax = self.parent_axes.get_xlim()
        ymin, ymax = self.parent_axes.get_ylim()

        xmid = 0.5 * (xmax + xmin)
        ymid = 0.5 * (ymax + ymin)

        dx = xmid - xmin
        dy = ymid - ymin

        theta = np.linspace(0.0, 2 * np.pi, 1000)
        self["c"].data = np.array(
            [xmid + dx * np.cos(theta), ymid + dy * np.sin(theta)]
        ).transpose()
        self["h"].data = np.array(
            [np.linspace(xmin, xmax, 1000), np.repeat(ymid, 1000)]
        ).transpose()
        self["v"].data = np.array(
            [np.repeat(xmid, 1000), np.linspace(ymin, ymax, 1000)]
        ).transpose()

        super().update_spines()

    def _update_patch_path(self):
        """Override path patch to include only the outer ellipse,
        not the major and minor axes in the middle.
        """
        self.update_spines()
        vertices = self["c"].data

        if self._path is None:
            self._path = Path(vertices)
        else:
            self._path.vertices = vertices

    def draw(self, renderer):
        """Override to draw only the outer ellipse,
        not the major and minor axes in the middle.

        FIXME: we may want to add a general method to give the user control
        over which spines are drawn.
        """
        axis = "c"
        pixel = self[axis]._get_pixel()
        line = Line2D(
            pixel[:, 0],
            pixel[:, 1],
            linewidth=self._linewidth,
            color=self._color,
            zorder=1000,
        )
        line.draw(renderer)