Positions/objects/items
APRS contains a number of packet types including position/object/item, status, messages, queries, weather reports and telemetry. The position/object/item packets contain the latitude and longitude, and a symbol to be displayed on the map, and have many optional fields for altitude, course, speed, radiated power, antenna height above average terrain, antenna gain, and voice operating frequency. Positions of fixed stations are configured in the APRS software. Moving stations (portable or mobile) automatically derive their position information from a GPS receiver connected to the APRS equipment.
The map display uses these fields to plot communication range of all participants and facilitate the ability to contact users during both routine and emergency situations. Each position/object/item packet can use any of several hundred different symbols. Position/objects/items can also contain weather information or can be any number of dozens of standardised weather symbols. Each symbol on an APRS map can display many attributes discriminated either by colour or other technique. These attributes are:
- Moving or fixed
- Dead-Reckoned or old
- Message capable or not
- Station, object or item
- Own object/item or other station object/item
- Emergency, priority, or special
Read more about this topic: Automatic Packet Reporting System
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