Trimble Outdoors SK8 - Manual (Page 57)

Lassen-SK8 Embedded GPS Module 4-5
Operation and Performance
4.3.4 PDOP Switch
The default positioning mode for the Lassen-SK8 is Automatic. In this mode, the receiver
attempts to generate a 3-dimensional (3D) position solution, when four or more satellites
meeting the mask criteria are visible. If such a satellite set cannot be found, the receiver
will automatically switch to 2-dimensional (2D) mode. The PDOP switch establishes the
trade-off between 3D positioning and PDOP. With the PDOP Switch set to 6, the receiver
will compute a 2D position with a HDOP below 6 rather than a 3D position with a PDOP
greater than 6, even when four or more satellites are visible.
*
Note – PDOP Switch is only used in Auto mode. If the PDOP Switch is greater than the
PDOP Mask, it will stay in 3D mode.
4.4 Standard Operating Modes
The tracking mode controls the allocation of the receiver's tracking channels and the
method used for computing position fixes. The output of GPS data is controlled by two
operating modes:
• Fix Modes (2D, 3D, or Automatic)
• Differential GPS Mode (On, Off, or Auto)
Each of these operating modes is described below.
4.4.1 Fix Modes
The Lassen-SK8 offers three positioning modes: 2D Manual, 3D Manual, and Automatic
2D/3D. Automatic 2D/3D is the default mode for the Lassen-SK8. The positioning mode
can be modified in receivers accepting TSIP commands. See Appendix A for more
information on the TSIP protocol.
2D Manual
In 2D Manual mode, the Lassen-SK8 will only generate 2-dimensional (2D) position
solutions (latitude and longitude only), regardless of the number of visible satellites. If the
altitude is not entered, the receiver uses mean sea level as the default altitude. The greater
the deviation between the actual and default altitudes, the greater the error in the 2D
position. For TSIP applications, enter local altitude in MSL/HAE via TSIP packet 2AH
(see Appendix A).
*
Note – 2D Manual mode is not recommended for differential GPS applications since any
deviation in altitude will cause a significant error in the latitude and longitude. Only use the
2D Manual mode for flat land or marine applications where the elevation is known or
constant. For DGPS applications, the 3D Manual mode is the recommended positioning
mode for the highest level of accuracy.