feature request

[bodewits]

This is a request for

• [ x ] a new feature
• an enhancement to existing sbpy functionality
• somethings else: [explain here]

The requested changes will be implemented by

• me
• [x ] the sbpy developers

High-level concept
Where is the sun and orbit vector; add pointy arrows to figures using the WCS.

Explain the relevance to sbpy
Almost every small body (comet) observation requires this feature

Proposal details
Use the WCS and information from Horizons to determine the directions.

Example (pseudo-)code
N/A

[github-actions]

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[mkelley]

Thanks, @bodewits!

I'm thinking that if we are using the WCS, then having something compatible with astropy's WCSAxes could make sense:

import matplotlib.pyplot as plt

import astropy.units as u
from astropy.wcs import WCS
from astropy.io import fits
from astropy.utils.data import get_pkg_data_filename

from sbpy.visualization import arrows

filename = get_pkg_data_filename('galactic_center/gc_msx_e.fits')

hdu = fits.open(filename)[0]
wcs = WCS(hdu.header)
fig, ax = plt.subplots(subplot_kw=dict(projection=wcs))
ax.imshow(hdu.data, vmin=-2.e-5, vmax=2.e-4, origin='lower')

location = [-22.5, -22.5] * u.arcmin
angles = [45, 120] * u.deg
labels = ("sun", "v")
arrows(ax, location, angles, labels=labels)

As a stretch goal, we could also do something with the Ephem class:

eph = Ephem.from_horizons("40P")
eph.arrows(ax, ["direction", "sun_angle", "velocity_angle"])