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Add ephemeris, docs for rotation; but, untested?

This commit is contained in:
Brandon Rhodes 2019-12-11 14:21:43 -05:00
parent e6f544d353
commit 6995fe446c
2 changed files with 30 additions and 4 deletions
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ci/moon_pa_de421_1900-2050.bpc Normal file
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jplephem/__init__.py
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@ -43,9 +43,9 @@ Command Line Tool
If you have downloaded a ``.bsp`` file, you can run ``jplephem`` from
the command line to display the data inside of it::
python -m jplephem comment de430.bsp
python -m jplephem dap de430.bsp
python -m jplephem spk de430.bsp
python -m jplephem comment de430t.bsp
python -m jplephem dap de430t.bsp
python -m jplephem spk de430t.bsp
You can also take a large ephemeris and produce a smaller excerpt by
limiting the range of dates that it covers::
@ -75,7 +75,7 @@ The recent DE430 ephemeris is a useful starting point. It weighs in at
115 MB, but provides predictions across the generous range of years
1550–2650:
http://naif.jpl.nasa.gov/pub/naif/generic_kernels/spk/planets/de430.bsp
https://naif.jpl.nasa.gov/pub/naif/generic_kernels/spk/planets/de430.bsp
After the kernel has downloaded, you can use ``jplephem`` to load this
SPK file and learn about the segments it offers:
@ -256,6 +256,32 @@ time of day. Nearly all ``jplephem`` routines accept this optional
``tdb2`` argument if you wish to provide it, thanks to the work of
Marten van Kerkwijk!
Support for Binary PCKs
-----------------------
You can also load and produce rotation matrices from a binary PCK file.
Its segments are available through the ``segments`` attributes of the
returned object.
>>> from jplephem.pck import PCK
>>> p = PCK.open('moon_pa_de421_1900-2050.bpc')
>>> p.segments[0].body
31006
>>> p.segments[0].frame
1
>>> p.segments[0].data_type
2
Given a solary system barycenter Julian date, the segment will return
the three angles necessary to build a rotation matrix: right ascension
of the pole, declination of the pole, and cumulative rotation of the
body’s axis. Typically these will all be in radians.
>>> np.set_printoptions(precision=6, suppress=True)
>>> tdb = 2454540.34103
>>> print(p.segments[0].compute(tdb, 0.0, False))
[ 0.039279 0.387836 3253.013946]
Legacy Ephemeris Packages
-------------------------