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vis_sample - Python Package for visibility sampling ==================================================== Purpose: vis_sample allows you to sample visibilities from a user-supplied sky-brightness image. (u,v) grid points can either be supplied by the user, or can be retrieved from a template uvfits file / measurement set. The results can be output either to a uvfits file or returned back to the user (for scripting) Parameters __________ imagefile : the input sky brightness image, needs to be in a valid FITS format with units of DEG for the RA and DEC or a RADMC3D image.out file (ascii format) for uv points use: uvfile - uvfits file or measurement set with visibilities that the sky brightness will be interpolated to OR uu, vv - numpy arrays - they need to be in units of lambda (i.e. number of wavelengths) mu_RA - right ascension offset from phase center in arcseconds mu_DEC - declination offset from phase center in arcseconds src_distance - distance to source in parsecs - only required for RADMC3D input images gcf_holder - (optional) gcf_holder object returned by previous call to vis_sample (see below return_gcf). If you use this option DO NOT feed in a uvfile or uu, vv arrays. They will be used by default and you'll see no speed increase corr_cache - (optional parameter) 2D corr_cache array output by previous call to vis_sample (see below return_corr_cache). outfile - name of optional output file, needs to have either a .uvfits or .ms extension consistent with extension of uvfile verbose - prints all progress output and timing return_gcf - (boolean) flag to return the gcf cache to allow faster interpolation for many models return_corr_cache - (boolean) flag to return the correction function cache to allow faster interpolation for many models Usage:: >> from vis_sample import vis_sample # import the vis_sample command >> vis_sample(imagefile="my_model.fits", uvfile="data.uvfits", outfile='interp.uvfits') # sample my_model using data (u,v) points and output to interp.uvfits >> interp_vis = vis_sample(imagefile="my_model.fits", uvfile="data.uvfits") # sample my_model using data (u,v) points, interp_vis stores visibilities In the second usage, interp_vis is the "raw" output visibility, ie just a numpy array of size [n_visibilities, n_chans] We can also output the caches for faster future usage: >> interp, gcf_holder = vis_sample(imagefile="my_model.fits", uvfile="data.uvfits", return_gcf = True) # sample my_model using data (u,v) points, also store the gcf_holder >> interp2 = vis_sample(imagefile="second_model.fits", gcf_holder = gcf_holder) # sample a second model using the same (u,v) points, this is faster now >> interp, gcf_holder, corr_cache = vis_sample(imagefile="my_model.fits", uvfile="data.uvfits", return_gcf = True, return_corr_cache = True) # sample my_model using data (u,v) points, also store the gcf_holder and corr_cache >> interp2 = vis_sample(imagefile="second_model.fits", gcf_holder = gcf_holder, corr_cache=corr_cache) # sample a second model using the same (u,v) points, this is faster now ================================= Source Structure ------------ Contents:: vis_sampler |-- vis_sample | |-- classes.py : Contains class information for visibilities and sky brightness images | |-- constants.py : Physical and numerical constants | |-- file_handling.py : File I/O | |-- gridding.py : Functions for the gcf and correction function | |-- interpolation.py : Functions for interpolating visibilities | |-- transforms.py : FFTs for sky brightness -> visibility | |-- vis_sampler.py : Wraps everything together into vis_sample() function | | | |-- __init__.py | |-- README
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