Source code for gammapy.utils.coordinates.fov

# Licensed under a 3-clause BSD style license - see LICENSE.rst
from astropy.coordinates import SkyCoord, SkyOffsetFrame

__all__ = ["fov_to_sky", "sky_to_fov"]


[docs]def fov_to_sky(lon, lat, lon_pnt, lat_pnt): """Transform field-of-view coordinates to sky coordinates. Parameters ---------- lon, lat : `~astropy.units.Quantity` Field-of-view coordinate to be transformed lon_pnt, lat_pnt : `~astropy.units.Quantity` Coordinate specifying the pointing position (i.e. the center of the field of view) Returns ------- lon_t, lat_t : `~astropy.units.Quantity` Transformed sky coordinate """ # Create a frame that is centered on the pointing position center = SkyCoord(lon_pnt, lat_pnt) fov_frame = SkyOffsetFrame(origin=center) # Define coordinate to be transformed. # Need to switch the sign of the longitude angle here # because this axis is reversed in our definition of the FoV-system target_fov = SkyCoord(-lon, lat, frame=fov_frame) # Transform into celestial system (need not be ICRS) target_sky = target_fov.icrs return target_sky.ra, target_sky.dec
[docs]def sky_to_fov(lon, lat, lon_pnt, lat_pnt): """Transform sky coordinates to field-of-view coordinates. Parameters ---------- lon, lat : `~astropy.units.Quantity` Sky coordinate to be transformed lon_pnt, lat_pnt : `~astropy.units.Quantity` Coordinate specifying the pointing position (i.e. the center of the field of view) Returns ------- lon_t, lat_t : `~astropy.units.Quantity` Transformed field-of-view coordinate """ # Create a frame that is centered on the pointing position center = SkyCoord(lon_pnt, lat_pnt) fov_frame = SkyOffsetFrame(origin=center) # Define coordinate to be transformed. target_sky = SkyCoord(lon, lat) # Transform into FoV-system target_fov = target_sky.transform_to(fov_frame) # Switch sign of longitude angle since this axis is # reversed in our definition of the FoV-system return -target_fov.lon, target_fov.lat