[aprssig] difference between Objects and Items?

Andrew P. andrewemt at hotmail.com
Wed Dec 10 17:58:55 EST 2014

Greetings, all.

I have a question for the long-time APRS wizards out there. What is the difference between an Object and an Item (other than the message format differences documented in the APRS Protocol Specification), and why would you choose one message format over the other to report a non-station entity? There doesn't seem to be much difference, conceptually speaking, between an Object with a timestamp set to the originating station's transmission time and an Item. Obviously, only Objects can be permanent, since only they can have timestamps set to the reserved code for permanence ("111111z").

Due to this ambiguity, I may have an error in my APRS client program, and I would like to correct this. Should the program infer use of Object format versus Item format for locally-originated entities from the permanence of the entity (or from other attributes), or explicitly require the user to specify which format to use? On a "take-over" of another station's Object or Item, should the Object versus Item characteristic be preserved in the take-over? Are Objects and Items in different namespaces (i.e., can you have an Object and an Item with the same name string and have them refer to distinct entities)?

Thanks in advance.

Andrew Pavlin, KA2DDO
author of YAAC ("Yet Another APRS Client")

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