Source code for ctapipe.coordinates.nominal_frame

The code in this module is basically a copy of

We are just not creating a metaclass and a factory but directly building the
corresponding class.
import astropy.units as u
from astropy.coordinates import (
from astropy.coordinates.matrix_utilities import matrix_transpose, rotation_matrix

__all__ = ["NominalFrame"]

[docs]class NominalFrame(BaseCoordinateFrame): """ Nominal coordinate frame. A Frame using a UnitSphericalRepresentation. This is basically the same as a HorizonCoordinate, but the origin is at an arbitray position in the sky. This is what astropy calls a SkyOffsetCoordinate If the telescopes are in divergent pointing, this Frame can be used to transform to a common system. Attributes ---------- origin: SkyCoord[AltAz] Origin of this frame as a HorizonCoordinate obstime: Tiem Observation time location: EarthLocation Location of the telescope """ frame_specific_representation_info = { UnitSphericalRepresentation: [ RepresentationMapping("lon", "fov_lon"), RepresentationMapping("lat", "fov_lat"), ] } default_representation = UnitSphericalRepresentation origin = CoordinateAttribute(default=None, frame=AltAz) obstime = TimeAttribute(default=None) location = EarthLocationAttribute(default=None) def __init__(self, *args, **kwargs): super().__init__(*args, **kwargs) # make sure telescope coordinate is in range [-180°, 180°] if isinstance(self._data, UnitSphericalRepresentation): self._data.lon.wrap_angle = Angle(180, unit=u.deg)
@frame_transform_graph.transform(FunctionTransform, NominalFrame, NominalFrame) def nominal_to_nominal(from_nominal_coord, to_nominal_frame): """Transform between two skyoffset frames.""" intermediate_from = from_nominal_coord.transform_to(from_nominal_coord.origin) intermediate_to = intermediate_from.transform_to(to_nominal_frame.origin) return intermediate_to.transform_to(to_nominal_frame) @frame_transform_graph.transform(DynamicMatrixTransform, AltAz, NominalFrame) def altaz_to_nominal(altaz_coord, nominal_frame): """Convert a reference coordinate to an sky offset frame.""" # Define rotation matrices along the position angle vector, and # relative to the origin. origin = nominal_frame.origin.represent_as(UnitSphericalRepresentation) mat1 = rotation_matrix(, "y") mat2 = rotation_matrix(origin.lon, "z") return mat1 @ mat2 @frame_transform_graph.transform(DynamicMatrixTransform, NominalFrame, AltAz) def nominal_to_altaz(nominal_coord, altaz_frame): """Convert an sky offset frame coordinate to the reference frame""" # use the forward transform, but just invert it mat = altaz_to_nominal(altaz_frame, nominal_coord) # transpose is the inverse because mat is a rotation matrix return matrix_transpose(mat)