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A-50 Acutime 2000 Synchronization Kit User Guide
Trimble Standard Interface Protocol
A
The Single-Precision LLA Position Fix variation of the packet
provides current GPS position fix in LLA (latitude, longitude, and
altitude) coordinates. If the I/O "position" option is set to "LLA" and
the I/O "precision-of-position output" is set to single-precision, and
the packet is masked with packet 8E-4D, then the receiver sends this
packet each time a fix is computed. The data format is shown below.
The LLA conversion is done according to the datum selected using
packet 8E-14. The default is WGS-84. Altitude is referred to the
WGS-84 ellipsoid or the MSL Geoid, depending on which I/O "LLA
altitude" option is selected. The time-of-fix is in GPS time or UTC,
depending on which I/O "timing" option is selected.
This packet also is sent at start-up with a negative time-of-fix to
report the current stored position. Packet 84 provides a double-
precision version of this information.
"
Caution – When converting from radians to degrees, significant and
readily visible errors will be introduced by use of an insufficiently
precise approximation for the constant
π(Pi). The value of the
constant Pi as specified in ICD-GPS-200 is 3.1415926535898.
The MSL option is only valid with the WGS-84 datum. When using
other datums, only the HAE option is valid.
Table A-40 Report Packet 4A – Report Single-Precision
LLA Position
Byte Item Type Units
0-3 Latitude SINGLE Radians; + for north,
- for south
4-7 Longitude SINGLE Radians; + for east,
- for west
8-11 Altitude SINGLE Meters
12-15 Clock Bias SINGLE Meters
6-19 Time-of-Fix SINGLE Seconds