I'm trying to convert the equatorial coordinates of an object to alt-az coordinates for a given time & location in (hopefully) <5 sec runtime, or more ideally, <1 sec runtime.
Following the astropy tutorial for coordinate transformations, I set up the following code:
from astropy import units as u
from astropy.coordinates import SkyCoord,EarthLocation, AltAz
from astropy.time import Time
target = SkyCoord(9.81625*u.deg, 0.88806*u.deg, frame='icrs')
location = EarthLocation(lat='31d57.5m', lon='-111d35.8m', height=0*u.m)
obs_time = Time('2010-12-21 1:00')
alt_az_frame = AltAz(location=location, obstime=obs_time)
target_alt_az = target.transform_to(alt_az_frame)
print(target_alt_az.alt, target_alt_az.az)
This code takes 20 seconds to run, almost all of which comes from the target.transform_to(alt_az_frame) line.
Is there a more appropriate way to use the transform_to function to speed up the code, or should I abandon using astropy altogether and write code from scratch? I understand there's a lot of extra functionality built into SkyCoord objects, much of which I likely don't need -- it's just convenient to use pre-built, standardized code.
After some debugging, it seems that it happens because astropy.utils.iers.iers's conf.iers_auto_url is a bad url. Here is my simple solution for your problem.
from astropy.utils.iers.iers import conf
# The desired url may change in the future
conf.iers_auto_url = 'ftp://cddis.gsfc.nasa.gov/pub/products/iers/finals2000A.all'
# Run your code here
Alternatively, you can do things like conf.remote_timeout = 0.1 or conf.auto_download = False(use backup data).
I couldn't find a document directly relevant to this issue but reading this page may help. This problem was discussed in the issue. I think this problem happens of only certain versions of the library, so updating the library to the latest version could be a solution.