Add excerpt to the command line
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Brandon Rhodes
parent
b5f23ddbe2
commit
dd51993296
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@ -37,16 +37,33 @@ JPL domain.
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Command Line Tool
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-----------------
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If you have downloaded a ``.bsp`` file and want to learn what ephemeris
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segments are stored inside of it, you can have ``jplephem`` print them
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out by invoking the module directly from the command line::
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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 de430.bsp
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python -m jplephem comment de430.bsp
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python -m jplephem dap de430.bsp
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python -m jplephem spk de430.bsp
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This will print out a summary identical to the one shown in the
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following section, but without requiring that you type and run any
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Python code.
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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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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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necessary to cover the dates you have specified. For example, the
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Jupiter satellite ephemeris `jup310.bsp` is famously large, weighing in
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a nearly a gigabyte in length. But if all you need are Jupiter's
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satellites for one month, you can download considerably less data:
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$ python -m jplephem excerpt 2018/1/1 2018/4/1 \
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https://naif.jpl.nasa.gov/pub/naif/generic_kernels/spk/satellites/jup310.bsp \
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excerpt.bsp
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$ ls -lh excerpt.bsp
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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, which took less than one minute.
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Getting Started With DE430
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--------------------------
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@ -5,6 +5,7 @@ from __future__ import print_function
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import argparse
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import sys
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from .daf import DAF
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from .excerpter import RemoteFile, write_excerpt
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from .spk import SPK
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def main(args):
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@ -33,9 +34,10 @@ def main(args):
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help="Create an SPK covering a narrower range of dates",
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)
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p.set_defaults(func=excerpt)
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p.add_argument('start_date', help='Start date yyyy/mm/dd')
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p.add_argument('end_date', help='End date yyyy/mm/dd')
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p.add_argument('file', help='Local filename or remote URL')
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p.add_argument('start_date', help='Start date yyyy/mm/dd', type=parse_date)
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p.add_argument('end_date', help='End date yyyy/mm/dd', type=parse_date)
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p.add_argument('path_or_url', help='Local filename or remote URL')
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p.add_argument('output_path', help='Output file to create')
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p = subparsers.add_parser(
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'spk',
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@ -68,8 +70,39 @@ def daf_segments(args):
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' '.join(repr(v) for v in values))
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def excerpt(args):
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pass
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if args.path_or_url.startswith(('http://', 'https://')):
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url = args.path_or_url
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f = RemoteFile(url)
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spk = SPK(DAF(f))
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with open(args.output_path, 'w+b') as output_file:
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write_excerpt(spk, output_file, args.start_date, args.end_date)
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else:
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path = args.path_or_url
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with open(path, 'rb') as f:
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spk = SPK(DAF(f))
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with open(args.output_path, 'w+b') as output_file:
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write_excerpt(spk, output_file, args.start_date, args.end_date)
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return ()
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def spk_segments(args):
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with open(args.path, 'rb') as f:
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yield str(SPK(DAF(f)))
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def parse_date(s):
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try:
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fields = [int(f) for f in s.split('/')]
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except ValueError:
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fields = []
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if len(fields) < 1 or len(fields) > 3:
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E = argparse.ArgumentTypeError
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raise E('specify each date as YYYY or YYYY/MM or YYYY/MM/DD')
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return julian_day(*fields)
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def julian_day(year, month=1, day=1):
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"""Given a proleptic Gregorian calendar date, return a Julian day int."""
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janfeb = month < 3
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return (day
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+ 1461 * (year + 4800 - janfeb) // 4
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+ 367 * (month - 2 + janfeb * 12) // 12
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- 3 * ((year + 4900 - janfeb) // 100) // 4
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- 32075)
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@ -0,0 +1,80 @@
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"""Extract data for a specific date range from an SPK file."""
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try:
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from urllib.request import URLopener
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except:
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from urllib import URLopener
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from numpy import copy
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from .daf import DAF
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from .spk import S_PER_DAY, T0
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clip_lower = max
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clip_upper = min
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def _seconds(jd):
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"""Convert a Julian Date to a number of seconds since J2000."""
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return (jd - T0) * S_PER_DAY
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def write_excerpt(input_spk, output_file, start_jd, end_jd):
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start_seconds = _seconds(start_jd)
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end_seconds = _seconds(end_jd)
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old = input_spk.daf
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# Copy the file record and the comments verbatim.
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f = output_file
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f.seek(0)
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f.truncate()
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for n in range(1, old.fward):
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data = old.read_record(n)
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f.write(data)
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# Start an initial summary and name block.
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summary_data = b'\0' * 1024
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name_data = b' ' * 1024
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f.write(summary_data)
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f.write(name_data)
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d = DAF(f)
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d.fward = d.bward = old.fward
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d.free = (d.fward + 1) * (1024 // 8) + 1
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d.write_file_record()
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# Copy over an excerpt of each array.
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for name, values in old.summaries():
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start, end = values[-2], values[-1]
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init, intlen, rsize, n = old.read_array(end - 3, end)
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rsize = int(rsize)
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i = int(clip_lower(0, (start_seconds - init) // intlen))
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j = int(clip_upper(n, (end_seconds - init) // intlen + 1))
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init = init + i * intlen
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n = j - i
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extra = 4 # enough room to rebuild [init intlen rsize n]
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excerpt = copy(old.read_array(
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start + rsize * i,
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start + rsize * j + extra - 1,
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))
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excerpt[-4:] = (init, intlen, rsize, n)
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values = (init, init + n * intlen) + values[2:]
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d.add_array(b'X' + name[1:], values, excerpt)
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class RemoteFile(object):
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def __init__(self, url):
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self.opener = URLopener()
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self.url = url
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self.offset = 0
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def seek(self, offset, whence=0):
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assert whence == 0
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self.offset = offset
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def read(self, size):
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start = self.offset
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end = start + size - 1
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assert end > start
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h = 'Range', 'bytes={}-{}'.format(start, end)
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self.opener.addheaders.append(h)
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data = self.opener.open(self.url).read()
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return data
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@ -3,23 +3,18 @@
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http://naif.jpl.nasa.gov/pub/naif/toolkit_docs/FORTRAN/req/spk.html
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"""
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from numpy import array, copy, empty, empty_like, rollaxis
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from numpy import array, empty, empty_like, rollaxis
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from .daf import DAF
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from .names import target_names
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T0 = 2451545.0
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S_PER_DAY = 86400.0
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clip_lower = max
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clip_upper = min
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def jd(seconds):
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"""Convert a number of seconds since J2000 to a Julian Date."""
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return T0 + seconds / S_PER_DAY
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def _seconds(jd):
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"""Convert a Julian Date to a number of seconds since J2000."""
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return (jd - T0) * S_PER_DAY
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class SPK(object):
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"""A JPL SPK ephemeris kernel for computing positions and velocities.
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@ -70,50 +65,6 @@ class SPK(object):
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"""Return the file comments, as a string."""
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return self.daf.comments()
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def excerpt(self, new_file, start_jd, end_jd):
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start_seconds = _seconds(start_jd)
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end_seconds = _seconds(end_jd)
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old = self.daf
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# Copy the file record and the comments verbatim.
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f = new_file
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f.seek(0)
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f.truncate()
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for n in range(1, old.fward):
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data = old.read_record(n)
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f.write(data)
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# Start an initial summary and name block.
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summary_data = b'\0' * 1024
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name_data = b' ' * 1024
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f.write(summary_data)
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f.write(name_data)
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d = DAF(f)
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d.fward = d.bward = old.fward
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d.free = (d.fward + 1) * (1024 // 8) + 1
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d.write_file_record()
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# Copy over an excerpt of each array.
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for name, values in old.summaries():
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start, end = values[-2], values[-1]
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init, intlen, rsize, n = old.read_array(end - 3, end)
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rsize = int(rsize)
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i = int(clip_lower(0, (start_seconds - init) // intlen))
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j = int(clip_upper(n, (end_seconds - init) // intlen + 1))
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init = init + i * intlen
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n = j - i
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extra = 4 # enough room to rebuild [init intlen rsize n]
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excerpt = copy(old.read_array(
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start + rsize * i,
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start + rsize * j + extra - 1,
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))
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excerpt[-4:] = (init, intlen, rsize, n)
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values = (init, init + n * intlen) + values[2:]
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d.add_array(b'X' + name[1:], values, excerpt)
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class Segment(object):
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"""A single segment of an SPK file.
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