Appendix-16
above 24 are allocated to on-orbit spares.
NOTE 4 Signal ID see Table below.
・DTM – Datum reference
$--DTM,ccc,a,x.x,a,x.x,a, x.x,ccc*hh<CR><LF>
1
2 3 4 5 6 7 8
1：L o cal datum(see Note 1)
WGS84 = W84 / WGS72 = W72 / SGS85 = S85 / PE90 = P90
User defined = 999 / IHO datum code (see Note 4)
2：Local datum subdivision code (see Note 2)
3：Lat offset, min, N/S (see Note 3)
4：Lat offset, min, N/S (see Note 3)
5：Lon offset, min, E/W (see Note 3)
6：Lon offset, min, E/W (see Note 3)
7：Altitude offset, m (see Note 3)
8：Reference datum (WGS84 = W84 / WGS72 = W72 / SGS85 = S85 / PE90 = P90)
NOTE 1 Three character alpha code for local datum. If not one of the listed earth-centred datums, or 999 for user
defined datums, use IHO datum code from International Hydrographic Organisation Publication S-60, Appendices B
and C. Null field if unknown. This field should be set to 999 when manual offsets are entered and in use by the
position fixing device.
NOTE 2 One character subdivision datum code when available or user defined reference character for user defined
datums, null field otherwise. Subdivision character from IHO Publication S-60, Appendices B and C.
NOTE 3 Latitude and longitude offsets are positive numbers, the altitude offset may be negative. Offsets change
with position: position in the local datum is offset from the position in the reference datum in the directions indicated:
P
local datum = Pref datum + offset
When field 1 contains a value of 999, these fields may not be null, and should contain the manually entered or user
defined offsets.
NOTE 4 Users should be aware that chart transformations based on IHO S60 parameters may result in significant
positional errors when applied to chart data.
・GBS – GNSS satellite fault detection
$--GBS, hhmmss.ss, x.x, x.x, x.x, xx, x.x, x.x, x.x, h, h *hh <CR><LF>
1
2 3 4 5 6 7 8 9 10
1：UTC time of the GGA or GNS fix associated with this sentence
2：Expected error in latitude (see Note 1)
3：Expected error in longitude (see Note 1)
4：Expected error in altitude (see Note 1)
5：ID number (see Note 2) of most likely failed satellite
6：Probability of missed detection for most likely failed satellite
7：Estimate of bias on most likely failed satellite(in metres)
8：Standard deviation of bias estimate
9：GNSS System ID (see Note 3)
10：GNSS Signal ID (see Note 4)
NOTE 1 Expected error in metres due to bias, with noise = 0.
NOTE 2 Satellite ID numbers. To avoid possible confusion caused by repetition of satellite ID numbers when using
multiple satellite systems, the following convention has been adopted (these legacy systems remain in effect for new
systems see NOTE 3):
a) GPS satellites are identified by their PRN numbers, which range from 1 to 32.
b) The numbers 33-64 are reserved for WAAS satellites. The WAAS system PRN numbers are 120-138.
The offset from WAAS SV ID to WAAS PRN number is 87. A WAAS PRN number of 120 minus 87
yields the SV ID of 33. The addition of 87 to the SV ID yields the WAAS PRN number.
c) The numbers 65-96 are reserved for GLONASS satellites. GLONASS satellites are identified by 64+
satellite slot number. The slot numbers are 1 through 24 for the full GLONASS constellation of 24
satellites; this gives a range of 65 through 88. The numbers 89 through 96 are available if slot numbers
above 24 are allocated to on-orbit spares.
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