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Fix numeric symbol overlays in compressed positions #98

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Fix numeric symbol overlays in compressed positions #98

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3d3d88c
Decode numeric overlays in compressed positions
infinitesniper Oct 25, 2026
e97f033
Cover compressed numeric overlays and unchanged symbol tables
infinitesniper Oct 25, 2026
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3 changes: 3 additions & 0 deletions aprslib/parsing/position.py
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Original file line number Diff line number Diff line change
Expand Up @@ -98,6 +98,9 @@ def parse_compressed(body):
body = body[13:]

symbol_table = compressed[0]
# APRS101: compressed numeric overlays use a-j instead of 0-9.
if 'a' <= symbol_table <= 'j':
symbol_table = chr(ord('0') + ord(symbol_table) - ord('a'))
symbol = compressed[9]

try:
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13 changes: 13 additions & 0 deletions tests/test_parse_position.py
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Expand Up @@ -166,5 +166,18 @@ def test_position_packet_optional_course(self):
_, result = parse_position(packet_type, packet)
self.assertEqual(expected, result)

class ParseCompressedPosition(unittest.TestCase):
def test_numeric_symbol_overlays(self):
for encoded, expected in zip('abcdefghij', '0123456789'):
_, result = parse_position('!', encoded + '5L!!<*e7#7P[')
self.assertEqual(expected, result['symbol_table'])
self.assertEqual('#', result['symbol'])

def test_other_symbol_tables(self):
for symbol_table in '/\\ABCDEFGHIJKLMNOPQRSTUVWXYZ':
_, result = parse_position('!', symbol_table + '5L!!<*e7#7P[')
self.assertEqual(symbol_table, result['symbol_table'])


if __name__ == '__main__':
unittest.main()