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GG Surveyor GPS+GLONASS Reference Manual
GPS and GLONASS System Time
GPS system time is equal to UTC time + the number of leap seconds added since
1980 (currently 12 seconds). GLONASS system time is equal to UTC time + 3 hours.
There is an additional GLONASS time shift relative to GPS time of approximately
-28.6 microseconds. Therefore, when UTC time equals 00:00:00.000000, GPS system
time equals 00:00:12.000000, and GLONASS system time equals 00:02:59.9999714.
In other words, GLONASS system time leads GPS system time by 3 hours minus the
number of leap seconds plus the sub-second time shift value, which is currently equal
to 2:59:47.9999714 (as of 30 June 1997).
GPS+GLONASS Standards
Two standards are used widely and successfully for GPS applications. These are
RTCM (Radio Technical Commission for Maritime Services) standard for
differential corrections
NMEA (National Marine Electronics Association) standard for reporting
position, velocity and satellite data.
Although both these standards were initially for marine use, they have been adopted
worldwide for all applications of GPS.
RTCM SC-104
The RTCM Special Committee 104 (SC-104) has defined differential correction
messages that are used worldwide for GPS. The messages that carry the GPS
Satellites per plane
4, unevenly spaced
8, evenly spaced
Orbital inclination
55°
64.8°
Orbital radius
26560 km
25510 km
Orbital period
11 hours 58 minutes
11 hours 15 minutes
NAVIGATION MESSAGE
Duration
12.5 minutes
2.5 minutes
Capacity
37500 bits
7500 bits
Time reference
UTC (US Naval Observatory)
UTC (SU, Russia)
Geodetic datum
WGS-84
PZ-90
Table A.1: Comparison of GPS and GLONASS (continued)
Parameter
GPS
GLONASS
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