csiborgtools/galomatch/units/transforms.py

# Copyright (C) 2022 Richard Stiskalek
# This program is free software; you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the
# Free Software Foundation; either version 3 of the License, or (at your
# option) any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General
# Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
"""
Various coordinate transformations.
"""


import numpy


little_h = 0.705
BOXSIZE = 677.7 / little_h  # Mpc. Otherwise positions in [0, 1].
BOXMASS = 3.749e19  # Msun


def cartesian_to_radec(arr, xpar="peak_x", ypar="peak_y", zpar="peak_z"):
    r"""
    Extract `x`, `y`, and `z` coordinates from a record array `arr` and
    calculate the radial distance :math:`r` in coordinate units, right
    ascension :math:`\mathrm{RA} \in [0, 360)` degrees and declination
    :math:`\delta \in [-90, 90]` degrees.

    Parameters
    ----------
    arr : record array
        Record array with the Cartesian coordinates.
    xpar : str, optional
        Name of the x coordinate in the record array.
    ypar : str, optional
        Name of the y coordinate in the record array.
    zpar : str, optional
        Name of the z coordinate in the record array.

    Returns
    -------
    dist : 1-dimensional array
        Radial distance.
    ra : 1-dimensional array
        Right ascension.
    dec : 1-dimensional array
        Declination.
    """
    x, y, z = arr[xpar], arr[ypar], arr[zpar]

    dist = numpy.sqrt(x**2 + y**2 + z**2)
    dec = numpy.rad2deg(numpy.arcsin(z/dist))
    ra = numpy.rad2deg(numpy.arctan2(y, x))
    # Make sure RA in the correct range
    ra[ra < 0] += 360

    return dist, ra, dec


def convert_mass_cols(arr, cols):
    r"""
    Convert mass columns from box units to :math:`M_{\odot}`. `arr` is passed
    by reference and is not explicitly returned back.

    Parameters
    ----------
    arr : structured array
        The array whose columns are to be converted.
    cols : str or list of str
        The mass columns to be converted.

    Returns
    -------
    None
    """
    cols = [cols] if isinstance(cols, str) else cols
    for col in cols:
        arr[col] *= BOXMASS


def convert_position_cols(arr, cols, zero_centered=True):
    r"""
    Convert position columns from box units to :math:`\mathrm{Mpc}`. `arr` is
    passed by reference and is not explicitly returned back.

    Parameters
    ----------
    arr : structured array
        The array whose columns are to be converted.
    cols : str or list of str
        The mass columns to be converted.
    zero_centered : bool, optional
        Whether to translate the well-resolved origin in the centre of the
        simulation to the :math:`(0, 0 , 0)` point. By default `True`.

    Returns
    -------
    None
    """
    cols = [cols] if isinstance(cols, str) else cols
    for col in cols:
        arr[col] *= BOXSIZE
        if zero_centered:
            arr[col] -= BOXSIZE / 2