Source code for sunpy.coordinates.offset_frame

import astropy.units as u
from astropy.coordinates import SkyOffsetFrame, SphericalRepresentation, UnitSphericalRepresentation

__all__ = ['NorthOffsetFrame']

[docs]class NorthOffsetFrame(object): """ A frame which is relative to some position and another frame. Based on `astropy.coordinates.SkyOffsetFrame` Coordinates in a NorthOffsetFrame are both centered on the position specified by the ``north`` keyword *and* they are oriented in the same manner as the ``north`` frame. Unlike `~astropy.coordinates.SkyOffsetFrame` a `NorthOffsetFrame` allows you to specify the position of the new north pole rather than the new origin to centre the new frame. Examples -------- A common use for this is to create a frame derived from Heliographic, which has the north pole at some point of interest. In this new frame, lines of longitude form great circles radially away from the point, and lines of latitude measure angular distance from the point. In this example the new frame is shifted so the new north pole is at (20, 20) in the Heliographic Stonyhurst frame. The new grid is overplotted in blue. .. plot:: :include-source: import matplotlib.pyplot as plt import astropy.units as u from astropy.coordinates import SkyCoord from sunpy.coordinates import NorthOffsetFrame import from import AIA_171_IMAGE m = north = SkyCoord(20*u.deg, 20*u.deg, frame="heliographic_stonyhurst") new_frame = NorthOffsetFrame(north=north) ax = plt.subplot(projection=m) m.plot() overlay = ax.get_coords_overlay('heliographic_stonyhurst') overlay[0].set_ticks(spacing=30. * u.deg, color='white') overlay.grid(ls='-', color='white') overlay = ax.get_coords_overlay(new_frame) overlay[0].set_ticks(spacing=30. * u.deg) overlay.grid(ls='-', color='blue') Notes ----- ``NorthOffsetFrame`` is a wrapper around the `~astropy.coordinates.SkyOffsetFrame` factory class. This class will calculate the desired coordianates of the ``origin`` from the ``north`` keyword argument and then create a `~astropy.coordinates.SkyOffsetFrame`. Using this frame is equivalent to using `~astropy.coordinates.SkyOffsetFrame` with ``lat = lat - 90*u.deg`` for a position of the north pole in the original northern hemisphere. This class will only work for Heliographic-Stonyhurst and Heliographic Carrington frames, and not helioprojective. If you want to rotate a helioprojective frame, it would be more natural to use the `~astropy.coordinates.SkyOffsetFrame`. """ def __new__(cls, *args, **kwargs): origin_frame = kwargs.pop('north', None) if origin_frame is None: raise TypeError("Can't initialize an NorthOffsetFrame without origin= keyword.") if hasattr(origin_frame, 'frame'): origin_frame = origin_frame.frame if not isinstance(, SphericalRepresentation): rep = origin_frame.represent_as(SphericalRepresentation) else: rep = lon = rep.lon lat = if lat > 0*u.deg: lat = lat - 90*u.deg rotation = None else: lon = lon - 180*u.deg lat = -90*u.deg - lat rotation = 180*u.deg if isinstance(, UnitSphericalRepresentation): new_rep = origin_frame.representation_type(lon=lon, lat=lat) else: new_rep = origin_frame.representation_type(lon=lon, lat=lat, distance=rep.distance) new_origin = origin_frame.realize_frame(new_rep) kwargs['origin'] = new_origin kwargs['rotation'] = rotation return SkyOffsetFrame(*args, **kwargs)