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#!/usr/bin/env python3
# Packs the Yale Bright Star Catalog (5th ed.) into public/assets/sky/stars.bin
# for the sky component: four little-endian float32s per star, right ascension
# and declination (J2000, radians), V magnitude and B-V colour index.
#
# curl -O http://tdc-www.harvard.edu/catalogs/bsc5.dat.gz
# python3 tools/sky/build-stars.py bsc5.dat.gz public/assets/sky/stars.bin
#
# Byte columns follow the catalog's ReadMe (CDS V/50).
import gzip
import math
import struct
import sys
def main(src, dst):
opener = gzip.open if src.endswith('.gz') else open
stars = []
with opener(src, 'rt', encoding='ascii', errors='replace') as f:
for line in f:
line = line.rstrip('\n').ljust(197)
if not line[75:77].strip() or not line[102:107].strip():
continue # the 14 entries that turned out not to be stars
ra = (int(line[75:77]) + int(line[77:79]) / 60 + float(line[79:83]) / 3600) * 15
dec = int(line[84:86]) + int(line[86:88]) / 60 + int(line[88:90]) / 3600
if line[83] == '-':
dec = -dec
vmag = float(line[102:107])
bv = float(line[109:114]) if line[109:114].strip() else 0.6
stars.append((math.radians(ra), math.radians(dec), vmag, bv))
with open(dst, 'wb') as out:
for s in stars:
out.write(struct.pack('<4f', *s))
print(f'{len(stars)} stars, {min(s[2] for s in stars):.2f} to {max(s[2] for s in stars):.2f} mag -> {dst}')
if __name__ == '__main__':
main(sys.argv[1], sys.argv[2])
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