Station Info, AIS ship names and icons

[Klaus Lohmann]

Hello everybody.

On my sailing boat "Bilbo" I operate an  APRS tracker, DJ8KL-8. First line  of "Stations near..."

On the same boat is an AIS transponder, which sends AIS messages to marinetraffic and, with the help of ais_jason.py, to http://aprs.fi/jsonais/post/......

Can anybody tell me, why some of the ship names are padded with @-signs and some are not?

All boats are displayed as motorboats, although there are AIS shiptypes 36 (Sailing vessel) and 37 (Pleasure Craft). But the programming of class B transponders is sometimes horrible. In Heiligenhafen we have a sailing boat with length 423m and beam 92m ;-)!

Greetings, Klaus, DJ8KL

[Eric, WB6TIX]

This is just a guess.

The vessel names where there are trailing @ symbols likely have the vessel name field prefilled with "null" characters and the name of the vessel overwrites the nulls.  If the vessel name is shorter than the field, the nulls are not overwritten and likely are being sent out in the  fixed size ASCII string.

 "null" and the various control characters can have undesired effects on the presentation of text, so downstream systems, including the application being used by the user can filter those characters out or can modify the characters to be some character that can be displayed.   Doing the latter makes the field a constant width.

One way of modifying the control characters is to set the most significant bit of the control characters.  Doing this to the ASCII "null" character turns it into a @ character.

Again, this is only a guess that is based on me doing this for a 1982 university computer programming class.

Eric, WB6TIX

[Klaus Lohmann]

Thank you, Eric. Sounds quite reasonable. Next weekend I will have access to my transponder,  fill the Name-Field with spaces and see, what happens.
KLaus, DJ8KL