makeBlendedCat.py

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"""Make a catalog of fakes that are highly blended."""
 
import os
import random
import argparse
 
import numpy as np
from astropy.table import Table, Column
 
 
def disturbRaDec(num, mu=0.6, sigma=0.6):
    """Disturb the coordinate a little bit."""
    return (np.random.normal(mu, sigma, num) / 3600.0)
 
 
def makeBlendedCat(fakeCat, realCat, raCol='ra', decCol='dec',
                   sigma=0.6, mu=0.6):
    """Make a highly blended version of fake catalog."""
    # Fake catalog
    if not os.path.isfile(fakeCat):
        raise Exception('# Can not find input fake catalog : %s' % fakeCat)
    else:
        fakeTab = Table.read(fakeCat, format='fits')
        nFake = len(fakeTab)
        print("# There are %d fake galaxies in the catalog" % nFake)
    # Name of the output catalog
    blendTab = fakeCat.replace('.fits', '_highb.fits')
 
    # Real catalog
    if not os.path.isfile(realCat):
        raise Exception('# Can not find input real catalog : %s' % realCat)
    else:
        realTab = Table.read(realCat, format='fits')
        nReal = len(realTab)
        print("# There are %d real galaxies in the catalog" % nReal)
 
    # Randomly select nFake galaxies from the realCat
    indices = random.sample(list(range(nReal)), nFake)
 
    # Replace the RA, DEC with a small shift
    fakeTab.add_column(Column(realTab[indices][raCol], name='RA_ori'))
    fakeTab.add_column(Column(realTab[indices][decCol], name='Dec_ori'))
 
    fakeTab['RA'] = (realTab[indices][raCol] + disturbRaDec(nFake,
                                                            mu=mu,
                                                            sigma=sigma))
    fakeTab['Dec'] = (realTab[indices][decCol] + disturbRaDec(nFake,
                                                              mu=mu,
                                                              sigma=sigma))
 
    # Save the new catalog
    fakeTab.write(blendTab, format='fits', overwrite=True)
 
    return fakeTab
 
 
if __name__ == '__main__':
 
    parser = argparse.ArgumentParser()
    parser.add_argument("fakeCat", help="Input catalog of fake objects")
    parser.add_argument("realCat", help="Catalog of real objects")
    parser.add_argument('--ra', '--raCol', dest='raCol',
                        help='Column for RA in realCat',
                        default='ra')
    parser.add_argument('--dec', '--decCol', dest='decCol',
                        help='Column for DEC in realCat',
                        default='dec')
    parser.add_argument('--mu', dest='mu',
                        help='mu of a normal distribution',
                        default=0.6, type=float)
    parser.add_argument('--sigma', dest='sigma',
                        help='sigma of a normal distribution',
                        default=0.6, type=float)
 
    args = parser.parse_args()
 
    makeBlendedCat(args.fakeCat, args.realCat,
                   raCol=args.raCol, decCol=args.decCol,
                   sigma=args.sigma, mu=args.mu)