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I'm looking at the raw packet data from http://aprs.fi. I see packets such as these:

ROSLDG>APN390,HEBOWX,OR2*,qAR,MKSRDG:@015805z4501.34NF12351.41W_000/000g000t053r000p000P000h92b......U2k 
W7KKE-9>TTRSUT,NEWPRT*,OR2-1,qAR,W7GC-3:'4]. {nv/]"3z}
KG7HEL-3>AAAPPP,WIDE1-1,WIDE2-1,qAR,BEAVRT:'vX<0x1c><0x1c> <0x1c>#/>TEMP1-1 digi running on battery= [Latitude and longitude are both 0]

Where is the specification for the information that comes after the : at the end of the path information? I can find a specification for APRS data as it is packeted into an AX.25 packet, but not for the messages that come from an APRS-IS server. Can I assume that anything after the : is in the same format as the Information Field in the APRS AX.25 specification? What happens to non-printables?

I've surmised that the ' and @ after the : are APRS Data Type Identifiers, but I have no idea what the <0x1c> stuff is in the last packet.

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Everything after the : is the payload that the station is sending out. While there are conventions so that the data is meaningful, I don't believe there are any standards. For example, the first line is a weather report, Wind calm (0 mph at 0 degrees, 0 mph gust), temp 54, no rain, RH 92% etc). The second line is probably a compressed location packet (compressed so that it takes less time to send.) In the last line, the <0x1c> probably represents a non-printable character (CTRL+Z or EOF). Since non-printable characters are, well, not printable the software either on the sending or receiving end likely converted the 0x1C (binary) to the string <0x1C> so that it would be printable (and if needed human readable.) Beyond that, without knowing the software sending the telemetry, there's not much more you can learn from it.

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  • $\begingroup$ Isn't there at least an APRS standard for the station's icon? Where is that data located? $\endgroup$
    – watkipet
    Jun 6, 2018 at 18:22
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    $\begingroup$ aprs.org/doc/APRS101.PDF describes it all. In the case of your example, I believe the icon is the /] in the second line, which according to Appendix 2 of the linked PDF means it's a BBS. $\endgroup$
    – Duston
    Jun 8, 2018 at 15:01

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