astra.utils.frames

astra.utils.frames#

Conversion between Astra’s internal ICRS coordinates and the mount’s frame.

Astra works in ICRS (J2000) everywhere: schedule ra/dec, SIMBAD lookups, JPL Horizons positions and the astrometric planet positions from astropy. A mount may expect a different frame. The ASCOM EquatorialSystem property says which one. Most modern drivers report equTopocentric, the apparent coordinates of date (JNow). Sending J2000 coordinates to such a mount misses by the precession since 2000, about 20 arcminutes in the mid 2020s.

The observatory reads EquatorialSystem once per mount and converts at the hardware boundary, just before a slew or sync. A mount that reports J2000, or whose property cannot be read, gets the ICRS coordinates unchanged.

Functions

from_mount_frame(ra_deg, dec_deg, system[, ...])

Convert a position read from the mount into ICRS.

needs_conversion(system)

Return True if coordinates must be transformed before reaching the mount.

parse_equatorial_system(value)

Parse an ASCOM enum value or a config string into an EquatorialSystem.

to_mount_frame(ra_deg, dec_deg, system[, ...])

Convert an ICRS position to the mount's frame.

Classes

EquatorialSystem(value)

ASCOM EquatorialCoordinateType values reported by EquatorialSystem.
class astra.utils.frames.EquatorialSystem(value)[source]#

Bases: IntEnum

ASCOM EquatorialCoordinateType values reported by EquatorialSystem.

OTHER = 0#
TOPOCENTRIC = 1#
J2000 = 2#
J2050 = 3#
B1950 = 4#
astra.utils.frames.parse_equatorial_system(value: object) → EquatorialSystem | None[source]#

Parse an ASCOM enum value or a config string into an EquatorialSystem.

Accepts the integer the driver returns (0 to 4) or a name such as “J2000” or “JNow”, in any case. Returns None for “auto”, for an unknown value, and for anything that is not an int or a str. None means “unknown, send ICRS unchanged”.

astra.utils.frames.to_mount_frame(ra_deg: float, dec_deg: float, system: EquatorialSystem | None, obstime: Time | None = None, location: EarthLocation | None = None) → tuple[float, float][source]#

Convert an ICRS position to the mount’s frame.

Parameters:

  • ra_deg – ICRS right ascension in degrees.

  • dec_deg – ICRS declination in degrees.

  • system – The mount’s EquatorialSystem. None, J2000 and OTHER return the input unchanged.

  • obstime – Time of the slew. Defaults to now. Needed for JNow and B1950.

  • location – Observer location. Improves the JNow result slightly.

Returns:

(ra_deg, dec_deg) in the mount’s frame.

astra.utils.frames.from_mount_frame(ra_deg: float, dec_deg: float, system: EquatorialSystem | None, obstime: Time | None = None, location: EarthLocation | None = None) → tuple[float, float][source]#

Convert a position read from the mount into ICRS. Inverse of to_mount_frame.

astra.utils.frames.needs_conversion(system: EquatorialSystem | None) → bool[source]#

Return True if coordinates must be transformed before reaching the mount.