from typing import Literal
import astropy.units as u # type: ignore[import-untyped]
import numpy as np
import numpy.typing as npt
from astropy.coordinates import SkyCoord # type: ignore[import-untyped]
from astropy.time import Time # type: ignore[import-untyped]
from pydantic import Field
from ...core.enums import ConstraintType
from ...ephemeris import Ephemeris
from .base import ConstraintABC, get_slice
[docs]
class EarthLimbConstraint(ConstraintABC):
"""
For a given Earth limb avoidance angle, is a given coordinate inside this
constraint?
Parameters
----------
name
The name of the constraint.
short_name
The short name of the constraint.
min_angle
The minimum angle from the Earth limb that the spacecraft can point.
Methods
-------
__call__(coord, ephemeris, earth_radius_angle=None)
Checks if a given coordinate is inside the constraint.
"""
[docs]
name: Literal[ConstraintType.EARTH] = ConstraintType.EARTH
[docs]
short_name: Literal["Earth"] = "Earth"
[docs]
min_angle: float | None = Field(
default=None, ge=0, le=180, description="Minimum angle from the Earth limb"
)
[docs]
max_angle: float | None = Field(
default=None, ge=0, le=180, description="Maximum angle from the Earth limb"
)
[docs]
def __call__(self, time: Time, ephemeris: Ephemeris, coordinate: SkyCoord) -> npt.NDArray[np.bool_]:
"""
Check for a given time, ephemeris and coordinate if positions given are
inside the Earth limb constraint. This is done by checking if the
separation between the Earth and the spacecraft is less than the
Earth's angular radius plus the minimum angle.
NOTE: Assumes a circular approximation for Earth.
Parameters
----------
coordinate : SkyCoord
The coordinate to check.
time : Time
The time to check.
ephemeris : Ephemeris
The ephemeris object.
Returns
-------
bool
`True` if the coordinate is inside the constraint, `False`
otherwise.
"""
# Find a slice what the part of the ephemeris that we're using
i = get_slice(time, ephemeris)
# Calculate the angular distance between the center of the Earth and
# the object. Note that creating the SkyCoord here from ra/dec stored
# in the ephemeris `earth` is 3x faster than just doing the separation
# directly with `earth`.
assert ephemeris.earth is not None and ephemeris.earth_radius_angle is not None
in_constraint = np.zeros(len(ephemeris.earth[i]), dtype=bool)
self.computed_values.earth_angle = SkyCoord(ephemeris.earth[i].ra, ephemeris.earth[i].dec).separation(
coordinate
)
if self.min_angle is not None:
in_constraint |= (
self.computed_values.earth_angle < ephemeris.earth_radius_angle[i] + self.min_angle * u.deg
)
if self.max_angle is not None:
in_constraint |= (
self.computed_values.earth_angle > ephemeris.earth_radius_angle[i] + self.max_angle * u.deg
)
# Return the result as True or False, or an array of True/False
return in_constraint