Add doctests to main test suite
Also, pivot to de421 since that ephemeris is already committed to the repository and so is available to tests.
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Brandon Rhodes
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@ -36,21 +36,20 @@ To learn more about SPK files, the official `SPK Required Reading
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document is available from the NAIF facility’s web site under the NASA
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JPL domain.
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Command Line Tool
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-----------------
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If you have downloaded a ``.bsp`` file, you can run ``jplephem`` from
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the command line to display the data inside of it::
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python -m jplephem comment de430t.bsp
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python -m jplephem dap de430t.bsp
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python -m jplephem spk de430t.bsp
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python -m jplephem comment de421.bsp
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python -m jplephem dap de421.bsp
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python -m jplephem spk de421.bsp
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You can also take a large ephemeris and produce a smaller excerpt by
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limiting the range of dates that it covers::
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python -m jplephem excerpt 2018/1/1 2018/4/1 de421.bsp outjup.bsp
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python -m jplephem excerpt 2018/1/1 2018/4/1 de421.bsp excerpt421.bsp
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If the input ephemeris is a URL, then `jplephem` will try to save
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bandwidth by fetching only the blocks of the remote file that are
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@ -66,38 +65,44 @@ few months, you can download considerably less data::
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-rw-r----- 1 brandon brandon 1.2M Feb 11 13:36 excerpt.bsp
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In this case only about one-thousandth of the ephemeris's data needed to
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be downloaded, a download which took less than one minute.
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be downloaded.
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Getting Started With DE430
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Getting Started With DE421
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--------------------------
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The recent DE430 ephemeris is a useful starting point. It weighs in at
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115 MB, but provides predictions across the generous range of years
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1550–2650:
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The DE421 ephemeris is a useful starting point. It weighs in at 17 MB,
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but provides predictions over the years 1900–2050:
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https://naif.jpl.nasa.gov/pub/naif/generic_kernels/spk/planets/de430.bsp
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https://naif.jpl.nasa.gov/pub/naif/generic_kernels/spk/planets/a_old_versions/de421.bsp
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After the kernel has downloaded, you can use ``jplephem`` to load this
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SPK file and learn about the segments it offers:
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>>> from jplephem.spk import SPK
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>>> kernel = SPK.open('de430.bsp')
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>>> kernel = SPK.open('de421.bsp')
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>>> print(kernel)
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File type DAF/SPK and format LTL-IEEE with 14 segments:
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2287184.50..2688976.50 Solar System Barycenter (0) -> Mercury Barycenter (1)
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2287184.50..2688976.50 Solar System Barycenter (0) -> Venus Barycenter (2)
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2287184.50..2688976.50 Solar System Barycenter (0) -> Earth Barycenter (3)
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2287184.50..2688976.50 Solar System Barycenter (0) -> Mars Barycenter (4)
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2287184.50..2688976.50 Solar System Barycenter (0) -> Jupiter Barycenter (5)
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2287184.50..2688976.50 Solar System Barycenter (0) -> Saturn Barycenter (6)
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2287184.50..2688976.50 Solar System Barycenter (0) -> Uranus Barycenter (7)
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2287184.50..2688976.50 Solar System Barycenter (0) -> Neptune Barycenter (8)
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2287184.50..2688976.50 Solar System Barycenter (0) -> Pluto Barycenter (9)
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2287184.50..2688976.50 Solar System Barycenter (0) -> Sun (10)
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2287184.50..2688976.50 Earth Barycenter (3) -> Moon (301)
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2287184.50..2688976.50 Earth Barycenter (3) -> Earth (399)
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2287184.50..2688976.50 Mercury Barycenter (1) -> Mercury (199)
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2287184.50..2688976.50 Venus Barycenter (2) -> Venus (299)
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File type DAF/SPK and format LTL-IEEE with 15 segments:
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2414864.50..2471184.50 Solar System Barycenter (0) -> Mercury Barycenter (1)
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2414864.50..2471184.50 Solar System Barycenter (0) -> Venus Barycenter (2)
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2414864.50..2471184.50 Solar System Barycenter (0) -> Earth Barycenter (3)
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2414864.50..2471184.50 Solar System Barycenter (0) -> Mars Barycenter (4)
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2414864.50..2471184.50 Solar System Barycenter (0) -> Jupiter Barycenter (5)
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2414864.50..2471184.50 Solar System Barycenter (0) -> Saturn Barycenter (6)
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2414864.50..2471184.50 Solar System Barycenter (0) -> Uranus Barycenter (7)
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2414864.50..2471184.50 Solar System Barycenter (0) -> Neptune Barycenter (8)
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2414864.50..2471184.50 Solar System Barycenter (0) -> Pluto Barycenter (9)
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2414864.50..2471184.50 Solar System Barycenter (0) -> Sun (10)
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2414864.50..2471184.50 Earth Barycenter (3) -> Moon (301)
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2414864.50..2471184.50 Earth Barycenter (3) -> Earth (399)
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2414864.50..2471184.50 Mercury Barycenter (1) -> Mercury (199)
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2414864.50..2471184.50 Venus Barycenter (2) -> Venus (299)
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2414864.50..2471184.50 Mars Barycenter (4) -> Mars (499)
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Since the next few examples involve vector output, let’s tell NumPy to
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make vector output attractive.
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>>> import numpy as np
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>>> np.set_printoptions(precision=3)
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Each segment of the file lets you predict the position of an object with
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respect to some other reference point. If you want the coordinates of
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@ -106,7 +111,7 @@ solar system, this ephemeris only requires you to take a single step:
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>>> position = kernel[0,4].compute(2457061.5)
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>>> print(position)
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[2.05700211e+08 4.25141646e+07 1.39379183e+07]
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[2.057e+08 4.251e+07 1.394e+07]
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But learning the position of Mars with respect to the Earth takes three
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steps, from Mars to the Solar System barycenter to the Earth-Moon
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@ -116,7 +121,7 @@ barycenter and finally to Earth itself:
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>>> position -= kernel[0,3].compute(2457061.5)
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>>> position -= kernel[3,399].compute(2457061.5)
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>>> print(position)
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[ 3.16065185e+08 -4.67929557e+07 -2.47554111e+07]
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[ 3.161e+08 -4.679e+07 -2.476e+07]
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You can see that the output of this ephemeris is in kilometers. If you
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use another ephemeris, check its documentation to be sure of the units
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@ -129,9 +134,9 @@ returned will itself be a vector as long as your date:
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>>> jd = np.array([2457061.5, 2457062.5, 2457063.5, 2457064.5])
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>>> position = kernel[0,4].compute(jd)
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>>> print(position)
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[[2.05700211e+08 2.05325363e+08 2.04928663e+08 2.04510189e+08]
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[4.25141646e+07 4.45315179e+07 4.65441136e+07 4.85517457e+07]
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[1.39379183e+07 1.48733243e+07 1.58071381e+07 1.67392630e+07]]
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[[2.057e+08 2.053e+08 2.049e+08 2.045e+08]
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[4.251e+07 4.453e+07 4.654e+07 4.855e+07]
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[1.394e+07 1.487e+07 1.581e+07 1.674e+07]]
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Some ephemerides include velocity inline by returning a 6-vector instead
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of a 3-vector. For an ephemeris that does not, you can ask for the
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@ -140,9 +145,9 @@ is delivered as a second return value:
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>>> position, velocity = kernel[0,4].compute_and_differentiate(2457061.5)
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>>> print(position)
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[2.05700211e+08 4.25141646e+07 1.39379183e+07]
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[2.057e+08 4.251e+07 1.394e+07]
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>>> print(velocity)
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[-363896.06287889 2019662.99596519 936169.77271558]
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[-363896.059 2019662.996 936169.773]
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The velocity will by default be distance traveled per day, in whatever
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units for distance the ephemeris happens to use. To get a velocity per
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@ -150,7 +155,7 @@ second, simply divide by the number of seconds in a day:
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>>> velocity_per_second = velocity / 86400.0
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>>> print(velocity_per_second)
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[-4.21175999 23.37572912 10.8352983 ]
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[-4.212 23.376 10.835]
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Details of the API
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------------------
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@ -183,8 +188,8 @@ provided above and read through the code to learn more.
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>>> segment = kernel[3,399]
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>>> print(segment.describe())
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2287184.50..2688976.50 Earth Barycenter (3) -> Earth (399)
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frame=1 data_type=2 source=DE-0430LE-0430
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2414864.50..2471184.50 Earth Barycenter (3) -> Earth (399)
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frame=1 data_type=2 source=DE-0421LE-0421
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* Each ``Segment`` loaded from the kernel has a number of attributes
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that are loaded from the SPK file:
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@ -210,7 +215,7 @@ provided above and read through the code to learn more.
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>>> initial_epoch, interval_length, coefficients = segment.load_array()
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>>> print(coefficients.shape)
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(3, 100448, 13)
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(3, 14080, 13)
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* The square-bracket lookup mechanism ``kernel[3,399]`` is a
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non-standard convenience that returns only the last matching segment
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@ -277,10 +282,9 @@ the three angles necessary to build a rotation matrix: right ascension
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of the pole, declination of the pole, and cumulative rotation of the
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body’s axis. Typically these will all be in radians.
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>>> np.set_printoptions(precision=6, suppress=True)
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>>> tdb = 2454540.34103
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>>> print(p.segments[0].compute(tdb, 0.0, False))
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[ 0.039279 0.387836 3253.013946]
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[3.928e-02 3.878e-01 3.253e+03]
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Legacy Ephemeris Packages
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-------------------------
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@ -151,7 +151,7 @@ class BaseSegment(object):
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class Segment(BaseSegment):
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"""Type 2 or type 3 segment."""
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# Type 2 or type 3 segment.
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def compute(self, tdb, tdb2=0.0):
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"""Compute the component values for the time `tdb` plus `tdb2`."""
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@ -9,7 +9,9 @@ smaller and more feature-oriented suite can be run with::
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"""
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import numpy as np
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import sys
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import tempfile
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from doctest import DocTestSuite, ELLIPSIS
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from functools import partial
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from io import BytesIO
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from jplephem import Ephemeris, commandline
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@ -424,3 +426,14 @@ File type NAIF/DAF and format BIG-IEEE with 15 segments:
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2433282.50..2469807.50 Venus Barycenter (2) -> Venus (299)
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2433282.50..2469807.50 Mars Barycenter (4) -> Mars (499)
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""")
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def load_tests(loader, tests, ignore):
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"""Run our main documentation as a test."""
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# Python 2.6 formats floating-point numbers a bit differently and
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# breaks the doctest.
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if sys.version_info >= (2, 7):
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tests.addTests(DocTestSuite('jplephem', optionflags=ELLIPSIS))
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return tests
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