utils/convert.py: Remove the slow, astropy.units based functions

1 files changed, 24 insertions, 64 deletions

diff --git a/fg21sim/utils/convert.py b/fg21sim/utils/convert.py
index 9eb9061..0fd08b4 100644
--- a/fg21sim/utils/convert.py
+++ b/fg21sim/utils/convert.py
@@ -5,75 +5,14 @@
 Utilities for conversion among common astronomical quantities.
 """
 
-import astropy.units as au
-
 from .units import (UnitConversions as AUC, Constants as AC)
 
 
-def Fnu_to_Tb(Fnu, omega, freq):
-    """
-    Convert flux density to brightness temperature, using the
-    Rayleigh-Jeans law, in the Rayleigh-Jeans limit.
-
-    Parameters
-    ----------
-    Fnu : `~astropy.units.Quantity`
-        Input flux density, e.g., `1.0*au.Jy`
-    omega : `~astropy.units.Quantity`
-        Source angular size/area, e.g., `100*au.arcsec**2`
-    freq : `~astropy.units.Quantity`
-        Frequency where the flux density measured, e.g., `120*au.MHz`
-
-    Returns
-    -------
-    Tb : `~astropy.units.Quantity`
-        Brightness temperature, with default unit `au.K`
-
-    References
-    ----------
-    - Brightness and Flux
-      http://www.cv.nrao.edu/course/astr534/Brightness.html
-    - Wikipedia: Brightness Temperature
-      https://en.wikipedia.org/wiki/Brightness_temperature
-    - NJIT: Physics 728: Introduction to Radio Astronomy: Lecture #1
-      https://web.njit.edu/~gary/728/Lecture1.html
-    - Astropy: Equivalencies: Brightness Temperature / Flux Density
-      http://docs.astropy.org/en/stable/units/equivalencies.html
-    """
-    equiv = au.brightness_temperature(omega, freq)
-    Tb = Fnu.to(au.K, equivalencies=equiv)
-    return Tb
-
-
 def Sb_to_Tb(Sb, freq):
     """
     Convert surface brightness to brightness temperature, using the
     Rayleigh-Jeans law, in the Rayleigh-Jeans limit.
 
-    Parameters
-    ----------
-    Sb : `~astropy.units.Quantity`
-        Input surface brightness, e.g., `1.0*(au.Jy/au.arcsec**2)`
-    freq : `~astropy.units.Quantity`
-        Frequency where the flux density measured, e.g., `120*au.MHz`
-
-    Returns
-    -------
-    Tb : `~astropy.units.Quantity`
-        Brightness temperature, with default unit `au.K`
-    """
-    omega = 1.0 * au.arcsec**2
-    Fnu = (Sb * omega).to(au.Jy)  # [Jy]
-    return Fnu_to_Tb(Fnu, omega, freq)
-
-
-def Sb_to_Tb_fast(Sb, freq):
-    """
-    Convert surface brightness to brightness temperature, using the
-    Rayleigh-Jeans law, in the Rayleigh-Jeans limit.
-
-    Avoid using `astropy.units` to optimize the speed.
-
         Tb = Sb * c^2 / (2 * k_B * nu^2)
 
     where `Sb` is the surface brightness density measured at a certain
@@ -81,6 +20,16 @@ def Sb_to_Tb_fast(Sb, freq):
 
     1 [Jy] = 1e-23 [erg/s/cm^2/Hz] = 1e-26 [W/m^2/Hz]
 
+    NOTE
+    ----
+    It is very easy to use ``astropy.units`` for the conversion:
+        equiv = au.brightness_temperature(omega, freq)
+        Tb = Fnu.to(au.K, equivalencies=equiv)
+
+    WARNING:
+    Using `astropy.units` for the conversion may be much slower.
+    This can be used as a cross check for the calculation.
+
     Parameters
     ----------
     Sb : float
@@ -95,6 +44,17 @@ def Sb_to_Tb_fast(Sb, freq):
     Tb : float
         Calculated brightness temperature
         Unit: [K]
+
+    References
+    ----------
+    - Brightness and Flux
+      http://www.cv.nrao.edu/course/astr534/Brightness.html
+    - Wikipedia: Brightness Temperature
+      https://en.wikipedia.org/wiki/Brightness_temperature
+    - NJIT: Physics 728: Introduction to Radio Astronomy: Lecture #1
+      https://web.njit.edu/~gary/728/Lecture1.html
+    - Astropy: Equivalencies: Brightness Temperature / Flux Density
+      http://docs.astropy.org/en/stable/units/equivalencies.html
     """
     # NOTE: [rad] & [sr] are dimensionless
     arcsec2 = AUC.arcsec2rad ** 2  # [sr]
@@ -104,7 +64,7 @@ def Sb_to_Tb_fast(Sb, freq):
     return Tb
 
 
-def Fnu_to_Tb_fast(Fnu, omega, freq):
+def Fnu_to_Tb(Fnu, omega, freq):
     """
     Convert flux density to brightness temperature, using the
     Rayleigh-Jeans law, in the Rayleigh-Jeans limit.
@@ -130,7 +90,7 @@ def Fnu_to_Tb_fast(Fnu, omega, freq):
         Unit: [K]
     """
     Sb = Fnu / omega  # [Jy/arcsec^2]
-    return Sb_to_Tb_fast(Sb, freq)
+    return Sb_to_Tb(Sb, freq)
 
 
 def JyPerPix_to_K(freq, pixelsize):
@@ -146,5 +106,5 @@ def JyPerPix_to_K(freq, pixelsize):
         The pixel size.
         Unit: [arcsec]
     """
-    factor = Fnu_to_Tb_fast(Fnu=1.0, omega=pixelsize**2, freq=freq)
+    factor = Fnu_to_Tb(Fnu=1.0, omega=pixelsize**2, freq=freq)
     return factor