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===== APX =====

APX is an experimental binary packet format for transmitting location information from a payload.

==== Packet Format ====

^ Offset ^ Name ^ Size ^ Description ^
|   0 | Packet Type    |   1 | 0x76 - Position |
|   1 | Callsign       |   6 | Callsign of the user / payload. The format is described below |
|   7 | Timestamp      |   5 | UTC timestamp |
|  12 | Latitude       |   4 | Latitude (-90 - 90 degrees, 0.000000042 degree accuracy, or ~0.46cm accuracy) |
|  16 | Longitude      |   4 | Longitude (-180 - 180 degrees, 0.000000084 degree accuracy, or ~0.93cm accuracy at the equator) |
|  20 | Altitude       |   3 | Altitude (-8388608 - 8388607 cm, or -83.8 - 83.8 km, two's compliment) |
|  23 | Fix Status     |   1 | 0 = No Fix, 1 = Fix, >= 2 undefined |
|  24 | PDOP           |   1 | Positional dilution of precision |
|  25 | Heading        |   1 | Heading (0 - 360 degrees, 1.4 degree accuracy) |
|  26 | Ground Speed   |   1 | Ground speed (0-100 m/s, 0.39 m/s accuracy) |
|  27 | Vertical Speed |   1 | Vertical speed (0-100 m/s, 0.39 m/s accuracy) |
|  28 | Checksum       |   4 | 32-bit CRC |
|  32 | FEC            |  32 | Reed-Solomon forward error correction data. This may be omitted for storage, or if the mode already provides FEC |

Sizes and offsets are in bytes, with each packet being 64 bytes in total (or 32 bytes with no FEC data).