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fix: pad AIS text fields with '@' instead of 0xff #459

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fix: pad AIS text fields with '@' instead of 0xff #459

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8 changes: 7 additions & 1 deletion lib/toPgn.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -551,9 +551,15 @@ fieldTypeWriters['BITLOOKUP'] = (pgn, field, value, bs) => {
}
}

// PGNs that carry AIS text. AIS pads its fixed-length text fields with '@'
// (ITU-R M.1371, Annex 8), and receivers strip that padding. Filling with 0xff
// instead leaves the fill bytes visible on some chart plotters, which render
// them as trailing spaces after the vessel name.
const AIS_STRING_PGNS = [129040, 129794, 129809, 129810]

fieldTypeWriters['STRING_FIX'] = (pgn, field, value, bs) => {
if (field.BitLength !== undefined) {
let fill = 0xff
let fill = AIS_STRING_PGNS.includes(pgn) ? 0x40 : 0xff
if (
(pgn === 129810 &&
(field.Name === 'Vendor ID' || field.Name === 'Callsign')) ||
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2 changes: 1 addition & 1 deletion test/pgns/129794.js
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,6 @@ module.exports = [
}
},
input:
'2017-04-15T14:58:37.235Z,6,129794,43,255,75,05,4a,ac,e4,15,00,00,00,00,57,44,44,39,31,37,31,41,54,4c,41,4e,54,49,43,20,43,4f,41,53,54,ff,ff,ff,ff,ff,ff,34,2c,01,46,00,00,00,5a,00,b7,44,00,e6,df,0c,a4,01,42,41,4c,54,49,4d,4f,52,45,ff,ff,ff,ff,ff,ff,ff,ff,ff,ff,ff,84,e1'
'2017-04-15T14:58:37.235Z,6,129794,43,255,75,05,4a,ac,e4,15,00,00,00,00,57,44,44,39,31,37,31,41,54,4c,41,4e,54,49,43,20,43,4f,41,53,54,40,40,40,40,40,40,34,2c,01,46,00,00,00,5a,00,b7,44,00,e6,df,0c,a4,01,42,41,4c,54,49,4d,4f,52,45,40,40,40,40,40,40,40,40,40,40,40,84,e1'
}
]
2 changes: 1 addition & 1 deletion test/pgns/129809.js
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,6 @@ module.exports = [
description: 'AIS Class B static data (msg 24 Part A)'
},
input:
'2019-04-15T15:16:46.572Z,6,129809,43,255,27,18,78,48,28,14,57,49,4c,48,45,4c,4d,ff,ff,ff,ff,ff,ff,ff,ff,ff,ff,ff,ff,ff,02,ff'
'2019-04-15T15:16:46.572Z,6,129809,43,255,27,18,78,48,28,14,57,49,4c,48,45,4c,4d,40,40,40,40,40,40,40,40,40,40,40,40,40,02,ff'
}
]
2 changes: 1 addition & 1 deletion test/pgns/129810.js
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,6 @@ module.exports = [
description: 'AIS Class B static data (msg 24 Part B)'
},
input:
'2023-07-22T13:41:17.102Z,6,129810,43,255,35,18,b5,59,29,14,25,47,41,52,4d,49,4e,ff,40,40,40,40,40,40,40,8c,00,0e,01,fa,00,3c,00,b6,59,29,14,20,01,ff'
'2023-07-22T13:41:17.102Z,6,129810,43,255,35,18,b5,59,29,14,25,47,41,52,4d,49,4e,40,40,40,40,40,40,40,40,8c,00,0e,01,fa,00,3c,00,b6,59,29,14,20,01,ff'
}
]