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.

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

 

 

 

 

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.

A-50

Acutime 2000 Synchronization Kit User Guide

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Trimble Outdoors Part Number 45005-00-ENG, AcutimeTM2000 Synchronization Kit manual Latitude