62 lines
2.0 KiB
Python
62 lines
2.0 KiB
Python
"""Parse data files from the International Earth Rotation Service.
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See:
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https://datacenter.iers.org/eop.php
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ftp://cddis.gsfc.nasa.gov/pub/products/iers/readme.finals2000A
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"""
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import numpy as np
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from ..constants import DAY_S
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inf = float('inf')
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# This regular expression must remain a plain string; attempting to
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# compile it triggers a bug in older NumPy versions like 1.14.3:
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# https://github.com/skyfielders/python-skyfield/issues/372
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_R = (b'(?m)^......(.........) . '
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b'(.\\d.......)......... '
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b'(.\\d.......)......... '
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b'.(.\\d........)')
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def parse_x_y_dut1_from_finals_all(f):
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return np.fromregex(f, _R, [
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('utc_mjd', float),
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('x_arcseconds', float),
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('y_arcseconds', float),
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('dut1', float),
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])
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def install_polar_motion_table(ts, finals_data):
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t = ts.utc(1858, 11, 17.0 + finals_data['utc_mjd'])
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ts.polar_motion_table = (
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t.tt,
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np.array(finals_data['x_arcseconds']),
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np.array(finals_data['y_arcseconds']),
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)
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def build_timescale_arrays(utc_mjd, dut1):
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big_jumps = np.diff(dut1) > 0.9
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leap_second_mask = np.concatenate([[False], big_jumps])
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tt_minus_utc = np.cumsum(leap_second_mask) + 32.184 + 12.0
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daily_tt = utc_mjd + tt_minus_utc / DAY_S + 2400000.5
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daily_delta_t = (tt_minus_utc - dut1).round(7)
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leap_dates = utc_mjd[leap_second_mask]
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# Since "finals2000A.all" starts on 1973-01-02 and leaves out the
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# first two leap seconds, add them back. (But check first, in case
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# the user loads a more complete data file than "finals2000A.all".)
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first_leap = leap_dates[0] if len(leap_dates) else 0
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more_leaps = [mjd for mjd in (41499.0, 41683.0) if first_leap > mjd]
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leap_dates = np.concatenate([more_leaps, leap_dates])
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leap_dates += 2400000.5
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leap_offsets = np.arange(11.0, len(leap_dates) + 11.0)
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return daily_tt, daily_delta_t, leap_dates, leap_offsets
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# Compatibility with older Skyfield versions:
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def parse_dut1_from_finals_all(f):
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data = parse_x_y_dut1_from_finals_all(f)
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return data['utc_mjd'], data['dut1']
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