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CNS Clock and Tac32
environments when more than eight satellites are visible, at the expense of
accuracy.
Geometry: Select from the list below to specify which DOP type to use for
satellite selection criteria. Default is PDOP.
Parameter
Definition
Geometry
Considered
GDOP
Geometric Dilution of Precision
4-D (3-D + time)
PDOP
Position Dilution of Precision
3-D
HDOP
Horizontal Dilution of Precision
2-D
VDOP
Vertical Dilution of Precision
1-D
TDOP
Time Dilution of Precision
Time
Iono Correction: Enables or disables the GPS receiver’s internal Ionospheric
correction algorithm. This algorithm is based on a simple model driven by
parameters provided from the GPS satellite's broadcast message.
Tropo Correction: Enables or disables the GPS receiver’s internal
Tropospheric correction algorithm. The algorithm used by the receiver is
unknown but is assumed to adjust the pseudorange values by the inverse of
the elevation angle (based on Dr. Tom Clark’s suppositions). The effect on
timing is likely to be only a few nanoseconds. Because this model is
undocumented and was not included in older receivers, this model is not
activated in the default timing mode.
Elevation Mask: The GPS receiver will attempt to track satellites for which
the elevation angle is greater than the satellite mask angle. This parameter
allows the user to control the elevation angle that is used for this decision.
App Type: This selection is used to change the receiver application type,
optimizing the search and reacquisition strategies for different applications.
The initial search time is the time the receiver spends searching for the
assumed visible satellites based on almanac and initial receiver position
(Reference Position). If the satellites are not found within this time the
receiver begins a systematic search for all satellites in the GPS constellation.
Application
Type
Max
Expected
Velocity
Velocity
Averaging
Approx
Initial Search
Time
Air
> 100 m/s
1 sec
15 min
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