Split file bundles in WMO’s FTP format
wmo_split.pl file(s)
WMO GTS combines many small files into larger files when transferring them via FTP to reduce the per-file overhead.
When working with meteorological data you might encounter this format when grabbing input files from a GTS live data stream.
The format is defined in WMO No. 386 Vol I “Manual on the Global Telecommunication System”, Attachment II-15, Section 4. TCP/IP, Subsection “FTP Procedures”.
Single files are prefixed by their length in bytes and a format identifier and then concatenated into the collection file.
| Bytes | Meaning |
|---|---|
| 8 | Message 1 length n₁ |
| 2 | Format identifier |
| n₁ | Message 1 |
| 8 | Message 2 length n₂ |
| 2 | Format identifier |
| n₂ | Message 2 |
The message itself consists of control characters, a sequence number, a heading and the content itself.
| Bytes | Meaning | Comment |
|---|---|---|
| 8 | Message 1 length n₁ | |
| 2 | Format identifier: ASCII “00” = Starting Line and End of Message present |
| *or* ASCII “01” = Starting Line and End of Message absent (deprecated) |
4 | SOH CR CR LF (= ASCII 01 13 13 10) | ⎫ 3 or 5 | sequence number as ASCII number | ⎪ | Heading | ⎬ Included in message length | Text | ⎪ 4 | CR CR LF ETX (= ASCII 13 13 10 03) | ⎭ 8 | Message 2 length n₂ | … | … |