Usage update from 3.1 -> 3.2

[telegraphic]

Is it still possible/reasonable to create an empty UVData object, then populate the attributes?

Previously (up until 3.1.3), I was able to create a blank UVData() object, and update parameters line by line, e.g.

uv = pyuvdata.UVData()
uv.Nbls            = md['n_baselines']
uv.Nblts           = md['n_baselines'] * md['n_integrations']

As of 3.2.0, this doesn't work:

uv = pyuvdata.UVData()
uv.Nants_telescope = 256

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Cell In[6], line 1
----> 1 uv.Nants_telescope = 256

AttributeError: property 'Nants_telescope' of 'UVData' object has no setter

It looks like this is due to using a Telescope() class at uv.telescope, but I'm not sure how this should be set up (the pyuvdata.Telescope.from_params() mentioned in the docs does not seem to exist). Is it still reasonable to create this as an empty Telescope() object and update the attributes?

[kartographer]

Hey @telegraphic - the telescope-based parameters were all previously deprecated back late in v2.4 I think, and as of v3.2 you can no longer access them straight off of the UVData object, but you can access them on the Telescope object that is now found on UVData.telescope:

In [1]: from pyuvdata import UVData

In [2]: uv = UVData()

In [3]: uv.telescope.Nants = 10

In [4]: uv.telescope.Nants
Out[4]: 10

You can similarly create an empty Telescope object, plug into it and attach that to UVData.telescope. Can't speak to what's reasonable versus not, but I can at least say that the above is certainly allowed!

[steven-murray]

@telegraphic I definitely recommend to instead use the UVData.new() method to construct your uvd objects, which sets a bunch of the attributes for you where possible, and has some reasonable defaults. Instead of having to remember every single attribute. But yes, you can still do it the old way.

[telegraphic]

Thanks @kartographer -- in that case, I think the only issue is that the telescope docs need an update as from_params() doesn't appear to be a thing

pyuvdata/docs/make_telescope.py

Line 33 in fa8cf9f

"arrays in memory using the :meth:`pyuvdata.Telescope.from_params`\n"

[telegraphic]

Thanks @steven-murray, will do!

FWIW here is a minimal example of creating a UVData object from scratch:

import pyuvdata

import numpy as np
from astropy import units as u
from astropy.coordinates import EarthLocation
from astropy.time import Time

# Create a location from the telescope
perth_eloc = EarthLocation.from_geodetic(lon=115 * u.deg, lat=-32 * u.deg)

# Dict of keys needed by Telescope.new()
# Note: instrument is optional, but needed at UVData() stage
telescope_params = {
 'name': 'Perthoscope',
 'location': perth_eloc,
 'instrument': 'HackSDR',
 'antenna_names': ['ant1', 'ant2', 'ant3'],
 'antenna_numbers': np.array([0,1,2]),
 'antenna_positions': np.array([[1,0,0], [0,1,0], [1,1,0]], dtype='float64')
}

# Now create a telescope object using the .new() method
tele = pyuvdata.Telescope.new(**telescope_params)

# Check the telescope passes basic validation
tele.check()

# Now we need to setup axes for the UVData object
freq_array = u.Quantity([1419, 1420, 1421], unit="MHz")
time_array = Time(["2025-01-01 12:01:00"], format="iso").jd      # Numpy array of Julian dates
polarization_array = np.array([-5, -6, -7, -8])   # (XX, YY, XY, YX) - see AIPS memo 117

# Dict of keys needed by UVData.new()
uvd_params = {
     'freq_array': freq_array,
     'times': time_array,   
     'polarization_array': polarization_array,
     'telescope': tele
     }

# Create the UVData object
uvd = pyuvdata.UVData.new(**uvd_params)

# And sanity check
uvd.check()

If this approach is sensible, may I suggest something similar is added to the tutorial (e.g. after this section)?

[steven-murray]

This looks great, thanks @telegraphic! I agree putting it into the docs where you suggested is a good idea. However I will defer to the Keeper of the Chronicles @bhazelton

[bhazelton]

I think we'd love to have anything in the tutorial that'd help users!

Maybe add something in this section: https://pyuvdata.readthedocs.io/en/latest/uvdata_tutorial.html#uvdata-instantiating-from-arrays-in-memory

Also happy to update the name/location of that section if it's too buried.