Setting up the IERS Bulletin A File#
The International Earth Rotation and Reference Systems Service (IERS) maintains a dataset of parameters that describe precisely how the Earth is oriented at any particular moment. AstroForge uses the IERS Bulletin A file for many coordinate conversion. You can find more information about this data on the IERS webpage, or download the data directly.
In most circumstances, AstroForge users do not need to explicitly setup the IERS file. The first time AstroForge does a coordinate conversion that requires IERS data it will try to download the file from the internet. This guide is to help when that process does not work for whatever reason.
Running AstroForge’s Automated Process#
The first troubleshooting step should be to re-run the automated process for downloading and installing the IERS file. To do so, simply run the following in python:
from astroforge.coordinates.iers import setup_iers
setup_iers(download=True)
If that is successful, you should see output that looks like the following (though the file paths will differ based on your system, username, and the current date):
>>> from astroforge.coordinates.iers import setup_iers
>>> setup_iers(download=True)
downloading IERS file from
https://datacenter.iers.org/data/9/finals2000A.all
Saving to /home/<USER>/.astroforge/data/finalsAll_2023-10-27.txt
[===========================================================================]
Making symbolic link to /home/<USER>/.astroforge/data/current_IERS_file.txt
Note
/home/<USER>/.astroforge/data.C:\Users\<USER>\.astroforge\data.If the progress bar never appears and the automated download process times out, check your internet connection and proxy settings— something is blocking python from reaching out to the internet. If that still doesn’t work, move on to the next section.
If the download and parsing succeeded, there should be some data files in the download
location. They consist of the raw IERS Bulletin A file (named finalsAll_<date>.txt),
three .npz files, and a symbolic link pointing current_IERS_file.txt to the latest
raw data file. The three .npz files are intermediate data products that were generated
by the automatic setup process.
Note
AstroForge never deletes old IERS files. It instead saves new files with the data and then updates the symbolic link.
$ ls -1 ~/.astroforge/data/
current_IERS_file.txt
finalsAll_2023-10-27.txt
leapsecond_data.npz
polarmotion_data.npz
ut1utc_data.npz
Manually Download and Install#
If the automated process isn’t working, you can try downloading and installing the IERS file yourself. The manual process isn’t that different than the automated one.
First, download the IERS file. Then, create the data directory:
$HOME/.astroforge/data on unix, or C:\Users\<USER>\.astroforge\data on windows.
Place the newly downloaded IERS file in the data directory and create a symbolic link to
it with the name current_IERS_file.txt. On unix, these steps can be achieved with
the following at the command line (remember to replace content in the angle brackets
with the actual IERS filename).
$ mkdir -p $HOME/.astroforge/data
$ cp <path/to/IERS/file> $HOME/.astroforge/data/
$ ln -s $HOME/.astroforge/data/<IERS_filename> $HOME/.astroforge/data/current_IERS_file.txt
Finally, launch python and parse the IERS data file manually:
from astroforge.coordinates.iers import setup_iers
setup_iers(download=False)
After parsing the raw datafile, the data directory should have the same .npz files shown
above. You can also test that it worked by using an AstroForge function that requires
these files, such as polarmotion():
>>> from astroforge.coordinates import polarmotion
>>> x, y = polarmotion(51720.0)
>>> print(x, y)
0.108198 0.28807
If none of these steps succeed, feel free to open a discussion about it on AstroForge’s discussion page.