State¶

class sbpy.dynamics.state.State(r: Quantity, v: Quantity, t: Quantity | Time, frame: FrameInputTypes | None = None)[source]¶

Bases: StateBase

Dynamical state.

Parameters:

rQuantity: Position (x, y, z), shape = (3,) or (N, 3).
vQuantity: Velocity (x, y, z), shape = (3,) or (N, 3).
tTime or Quantity: Time, a scalar or shape = (N,). Time as a Quantity may only be used with the ArbitraryFrame coordinate frame.
frameBaseCoordinateFrame class or string, optional: Reference frame for r and v. Default: ArbitraryFrame.

Notes

State data is immutable.

Examples

>>> from astropy.time import Time
>>> import astropy.units as u
>>> from sbpy.dynamics import State
>>> r = [1e9, 1e9, 0] * u.km
>>> v = [0, 0, 10] * u.km / u.s
>>> t = Time("2022-07-24", scale="tdb")
>>> state = State(r, v, t)

Or, specify time relative to an arbitrary epoch:

>>> t = 327 * u.day
>>> state = State(r, v, t)

Attributes Summary

`arbitrary_time`	True if the time attribute is arbitrary.
`frame`
`r`	Position vector.
`rv`	Position in km, and velocity in km/s.
`t`	Time.
`v`	Velocity vector.
`v_x`	x component of the velocity vector.
`v_y`	y component of the velocity vector.
`v_z`	z component of the velocity vector.
`x`	x component of the position vector.
`y`	y component of the position vector.
`z`	z component of the position vector.

Methods Summary

`from_ephem`(eph[, frame])	Initialize from an `Ephem` object.
`from_skycoord`(coords)	Initialize from astropy `SkyCoord`.
`from_states`(states)	Initialize from a list of states.
`observe`(target)	Project a target's position onto the sky.
`to_skycoord`()	Convert to a `SkyCoord` object.
`transform_to`(frame)	Transform state into another reference frame.

Attributes Documentation

arbitrary_time¶: True if the time attribute is arbitrary.

frame¶

r¶: Position vector.

rv¶: Position in km, and velocity in km/s.

t¶: Time.

v¶: Velocity vector.

v_x¶: x component of the velocity vector.

v_y¶: y component of the velocity vector.

v_z¶: z component of the velocity vector.

x¶: x component of the position vector.

y¶: y component of the position vector.

z¶: z component of the position vector.

Methods Documentation

classmethod from_ephem(eph: Ephem, frame: FrameInputTypes | None = None) → Self[source]¶

Initialize from an Ephem object.

Parameters:

eph~sbpy.data.ephem.core.Ephem: Ephemeris object, must have time, position, and velocity. Position and velocity may be specified using (“x”, “y”, “z”, “vx”, “vy”, and “vz”), or (“ra”, “dec”, “Delta”, “RA*cos(Dec)_rate”, “Dec_rate”, and “deltadot”).
framestring or BaseCoordinateFrame, optional: The reference frame for the ephemeris.

classmethod from_skycoord(coords: SkyCoord) → Self[source]¶

Initialize from astropy SkyCoord.

Parameters:

coords: ~astropy.coordinates.SkyCoord: The object state. Must have position and velocity, obstime, and be convertible to cartesian (3D) coordinates.

classmethod from_states(states: Iterable[Self]) → Self[source]¶

Initialize from a list of states.

The resulting reference frame will be that of states[0].

Parameters:

statesarray

observe(target: Self) → SkyCoord[source]¶

Project a target’s position onto the sky.

Parameters:

targetState: The target to observe.

Returns:

coordsSkyCoord

to_skycoord() → SkyCoord¶: Convert to a SkyCoord object.

transform_to(frame: FrameInputTypes) → Self¶

Transform state into another reference frame.

Parameters:

framestring or BaseCoordinateFrame: Transform into this reference frame.

Returns:

stateState: The transformed state.

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State¶