outfly/build/generate_starchart.py

#!/usr/bin/env python
# This script requires the following file in the extra/ directory:
# https://github.com/astronexus/HYG-Database/blob/cbd21013d2bb89732b893be357a6f41836dbe614/hyg/CURRENT/hygdata_v41.csv

import csv
import sys
import math
import re

PATH = "extra/hygdata_v41.csv"

#def entry(ra_hour, ra_min, ra_sec, dec_deg, dec_min, dec_sec, mag, name, color_index):
#    return [
#        ra_hour*15 + ra_min*0.25 + ra_sec*0.004166,
#        dec_deg + dec_min/60 + dec_sec/3600,
#        mag,
#        name,
#        color_index,
#    ]
#
#
#CUSTOM_ENTRIES = [
#    entry(0, 42, 44.3, 41, 16, 9, 3.44-15, 0.63, "Andromeda Galaxy"),
#]

# Lower apparent magnitude = brighter.
# Sun = -26.7
# Sirius = -1.44
# Betelgeuse = 0.45
# Polaris (north star) = 1.97
# Meissa (orion's head, 8th brightest star in orion) = 3.33
MAX_APPARENT_MAGNITUDE = 7.0

SOL_ABSMAG = 4.83
SOL_RADIUS = 696.3e6
SOL_LUMINOSITY = 3.828e26
STEFAN_BOLTZMANN_CONSTANT = 5.670374419e-8

print("// This file was autogenerated by \"genrate_starchart.py\" using data from the")
print("// HYG database: https://github.com/astronexus/HYG-Database/tree/main/hyg")
print("// License: CC BY-SA 4.0: https://creativecommons.org/licenses/by-sa/4.0/")
print("// Each star's values: (x, y, z, magnitude, absolute magnitude, color index, name)")
print("[")


def render(i, x, y, z, ra, dec, mag, absmag, ci, dist, name):
    # Takes ra/deg in degrees
    ra = float(ra)
    dec = float(dec)
    mag = float(mag)
    x, y, z = float(x), float(y), float(z)
    name = re.sub(r'\s+', ' ', name)
    if name == 'Sol':
        return

    #radius = star_radius(float(ci), float(absmag))

#    distance = 1.0
#    ra_radians = math.radians(ra * 15)  # ra is in [0, 24], multiplying by 15 gives degrees in [0, 360]
#    dec_radians = math.radians(dec)
#    #print(f"ra_radians={ra_radians}, dec_radians={dec_radians}, dec={dec}, ra={ra}", file=sys.stderr)
#    x = distance * math.cos(dec_radians) * math.cos(-ra_radians)
#    y = distance * math.cos(dec_radians) * math.sin(-ra_radians)
#    z = distance * math.sin(dec_radians)
#
#    # Correct for differences in coordinate system axes
#    x, y, z = x, z, y

    #brightness = 2.512 ** (0 - mag)

    print(f'({x:.04},{y:.04},{z:.04},{mag:.04},{absmag:.04},{ci},"{name}"),')


def clean_name(string):
    return "".join([c for c in string if c.isalnum() or c in ' -_'])


def star_radius(color_index, absolute_magnitude):
    # Convert color index to temperature (using Ballesteros' formula approximation for B-V)
    temp = 4600 * ((1 / (0.92 * color_index + 1.7)) + (1 / (0.92 * color_index + 0.62)))

    # Convert absolute magnitude to luminosity (in solar luminosities)
    lum = 10 ** (0.4 * (SOL_ABSMAG - absolute_magnitude))

    # Calculate the radius using Stefan-Boltzmann law (output should be in meters)
    radius = math.sqrt(lum * SOL_LUMINOSITY / (4 * math.pi * STEFAN_BOLTZMANN_CONSTANT * temp ** 4))  # Luminosity in watts for the Sun ~ 3.828e26

    # Convert radius from meters to solar radii (1 solar radius ≈ 6.96e8 meters)
    radius_solar = radius / SOL_RADIUS

    return radius_solar


total = 0
count = 0
count_extra = 0
entries = []
with open(PATH, "r", encoding="utf-8") as f:
    for index, entry in enumerate(csv.DictReader(f)):
        entries.append((index, entry))

entries.sort(key=lambda entry: float(entry[1]['mag']))

for index, entry in entries:
    total += 1
    ra = entry['ra']
    dec = entry['dec']
    x = entry['x']
    y = entry['y']
    z = entry['z']
    mag = entry['mag']
    absmag = entry['absmag']
    ci = entry['ci']
    dist = entry['dist']
    name = clean_name(entry['proper'])
    if not name:
        name = clean_name(entry['bf'])
    if not name:
        name = clean_name(entry['gl'])

    if not all([ra, dec, mag, ci]):
        continue
    if float(mag) > MAX_APPARENT_MAGNITUDE:
        continue
    render(index, x, y, z, ra, dec, mag, absmag, ci, dist, name)
    count += 1
#for entry in CUSTOM_ENTRIES:
#    render(entry[0], entry[1], entry[2], entry[3], entry[4])
#    count_extra += 1

print("]")
print(f"Wrote {count} stars (total={total}) + {count_extra} extra entries.", file=sys.stderr)