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# Copyright (c) 2016 Zhixian MA <zxma_sjtu@qq.com>
# MIT license
"""
Basic parameters to be used in point sources simulation.
References
----------
[1] Angular diameter distance,
https://en.wikipedia.org/wiki/Angular_diameter_distance
[2] FlatLambdaCDM,
{http://docs.astropy.org/en/stable/api/astropy.cosmology.
FlatLambdaCDM.html#astropy.cosmology.FlatLambdaCDM}
"""
from astropy.cosmology import FlatLambdaCDM
class PixelParams():
"""
A class to transform cosmology distance to angles or pixels.
Parameters
------------
H0: float
The hubble constant at z = 0, whose unit is km/s/Mpc
Om0: float
The total matter density.
ang_res: float
Angular resolution, i.e. degree per pixel. (May be useless)
ang_total: list
Total angles of the simulated sky region, whose unit is degree
z : float
Redshift
scale: float
The real object scale.
Example
------------
>>> PixelParams = PixelParams(img_size=(1024,1024),ang_total=(5,5))
"""
# Hubble constant at z = 0
H0 = 71.0
# Omega0, total matter density
Om0 = 0.27
# Redshift
z = 0.0
# Cosmology calculator
cosmo = 0.0
# angular diameter distance, [Mpc]
dA = 0.0
# angular resolution
ang_res = 0.0
def __init__(self, z=0.0):
self.z = z
self.cosmo = FlatLambdaCDM(H0=self.H0, Om0=self.Om0)
# angular diameter distance, [Mpc]
self.dA = self.cosmo.angular_diameter_distance(self.z).value
def get_angle(self, scale=1.0):
"""
Input real object scale, and output the respect observed
angle, and pixels.
"""
ang = scale / self.dA # [rac]
return ang
def get_scale(self, ang=1.0):
"""
Input real observed scale, and output the respect
real object scale, and pixels.
"""
scale = ang * self.dA # [Mpc]
return scale
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