Thursday, October 8, 2009

Status and comment texts

As a little early morning exercise I've made show the status message in the info balloon of the current position on the real-time map, and also in the KML. Status message is shown in purple, and the comment text is shown in green.

There has been some confusion about these messages. There are three kinds of "status/comment" messages you can attach to your position. For example, SM4IVE-9 (info) is sending two of them.

The comment text is sent together with the position, in the end of the position packet. Here's an example packet with a comment text of


The status message is sent as a separate packet which starts with a '>' character:


The Mic-E status message is encoded in a mic-e packet using just a few bits, and can contain one of these 8 standard messages: Off duty, En route, In service, Returning, Committed, Special, Priority, Emergency. 7 custom messages (Custom 0 to Custom 6) are also defined. All Mic-E packets contain this status message, and it only consumes a couple of bits in the message, so this requires the least bandwidth from the APRS channel. On the other hand, it can only express the few predefined values.

I would recommend using only the comment text, since it is sent in a single packet together with the position. The status message is sent in a separate packet which increases congestion.

If a status message is required (for example, if the text really needs to be so long that it doesn't fit in the comment text), the status message should not be sent too often. Certainly not as often as the position packet.

In the following photo Armi frowns upon seeing a long, static status packet:

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