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For #407, explain that open() does not re-download

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Brandon Rhodes 2020-07-17 06:08:15 -04:00
parent 5d17b96fcb
commit b8fdc4dc4a
1 changed files with 12 additions and 0 deletions
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skyfield/documentation/kepler-orbits.rst
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@ -48,6 +48,12 @@ To build a dataframe of comets:
864 comets loaded
Since the comets file has no explicit expiration date,
``load.open()`` will only download the file once.
Subsequent calls re-open the copy of the file already on your filesystem.
To force a fresh download and receive updated orbits and new comets,
pass ``reload=True``.
To generate a comet’s position,
first select its row from dataframe.
There are several Pandas techniques for selecting rows,
@ -157,6 +163,12 @@ The same four asteroid orbits could then be extracted with::
python mpc_make_excerpt.py 00001 00002 00003 00004 > MPCORB.excerpt.DAT
Note that the minor planets file has no explicit expiration date,
so ``load.open()`` in the above script
will only download the file once.
Subsequent calls re-open the copy of the file already on your filesystem.
To force a fresh download, pass ``reload=True``.
In either case, the resulting file — shorn of its text header,
and containing only minor planet orbits —
is ready for Skyfield to load.