Coding Coarse Position Data in National Location Protocol

Bits 59 to 85 of national location protocol beacons are used for coding course position data as described below.

The default settings to be used if location data is not available are as follows:

Bits 59 to 71 = "0 111 111 100 000"
Bits 72 to 85 = "0 111 111 110 000 0"

Note: Latitude and longitude data are rounded off (i.e. not truncated) to the available resolution. The initial coarse position encoded in the first protected data field (PDF-1) is selected to be as close to possible to the actual position. See table below for an example:

Real Position Position Encoded in Beacon

43 deg : 31 min : 56 sec North 43 deg : 32 min North

01 deg : 25 min : 32 sec East 01 deg : 26 min East

See the example depicting the assignment of bits in PDF-1 for encoding the location above.

National Location Protocols provide for higher resolution information to be encoded in the second protected data field (PDF-2) as a latitude and longitude offset relative to the coarse position provided in PDF-1.