GIFTS Spacecraft Frame (gdt.missions.gifts.frame)

Note

The GIFTS spacecraft frame implementation and this document are currently based on those provided by the Fermi Gamma-ray Data Tools, and will be revised in future versions.

The GIFTS spacecraft frame, GiftsFrame, is the frame that is aligned with the GIFTS spacecraft coordinate frame, and is represented by a quaternion that defines the rotation from spacecraft coordinates to the ICRS coordinate frame. This frame takes advantage of the Astropy coordinate frame design, so we can use the GiftsFrame to convert Astropy SkyCoord objects between the GiftsFrame and any celestial frame.

While the GiftsFrame is typically initialized when reading from a mission position history file (e.g. GiftsPosHist) instead of manually by a user, we can manually define the frame with a Quaternion:

>>> from gdt.core.coords import Quaternion
>>> from gdt.missions.gifts.frame import *
>>> quat = Quaternion([-0.218,  0.009,  0.652, -0.726], scalar_first=False)
>>> gifts_frame = GiftsFrame(quaternion=quat)
>>> gifts_frame
<GiftsFrame: 1 frames;
obstime=[J2000.000]
obsgeoloc=[(0., 0., 0.) m]
obsgeovel=[(0., 0., 0.) m / s]
quaternion=[(x, y, z, w) [-0.218,  0.009,  0.652, -0.726]]>

Notice that we can also define the frame with an obstime, which is useful for transforming between the GiftsFrame and a non-inertial time-dependent frame; an obsgeoloc, which can define the spacecraft location in orbit; and obsgeovel, which defines the spacecraft orbital velocity.

Now let us define a SkyCoord in RA and Dec:

>>> from astropy.coordinates import SkyCoord
>>> coord = SkyCoord(100.0, -30.0, unit='deg')

This can be rotated into the GIFTS frame with the following:

>>> gifts_coord = coord.transform_to(gifts_frame)
>>> (gifts_coord.az, gifts_coord.el)
(<Longitude [200.39733555] deg>, <Latitude [-41.88750942] deg>)

We can also transform from the GIFTS frame to other frames. For example, we define a coordinate in the GIFTS frame this way:

>>> gifts_coord = SkyCoord(50.0, 25.0, frame=gifts_frame, unit='deg')

Now we can tranform to ICRS coordinates:

>>> gifts_coord.icrs
<SkyCoord (ICRS): (ra, dec) in deg
    [(313.69000519, 26.89158349)]>

or Galactic coordinates:

>>> gifts_coord.galactic
<SkyCoord (Galactic): (l, b) in deg
    [(71.5141302, -11.56931006)]>

or any other coordinate frames provided by Astropy.

Reference/API

gdt.missions.gifts.frame Module

Functions

gifts_to_icrs(gifts_frame, icrs_frame)	Convert from the GIFTS frame to the ICRS frame.
icrs_to_gifts(icrs_frame, gifts_frame)	Convert from the ICRS frame to the GIFTS frame.

Classes

GiftsFrame(*args[, copy, ...])

The GIFTS spacecraft frame in azimuth and elevation.

Class Inheritance Diagram