2 Operation Details
network of reference stations and broadcast in real time by geostationary satellites in the L
band.
2.4.4.1
PPP Seeding
PPP provides centimeter-level position accuracy, but suffers from a relatively long conver-
gence time that can reach 15 to 20 minutes depending on the local multipath environment.
The convergence time can be dramatically reduced by feeding the known position into the
PPP engine. This process is referred to as PPP seeding, and the position fed into the PPP
engine is called the PPP seed. The receiver supports two seeding modes:
Manual Seeding:
in manual seeding, the user provides the accurate marker position (see
section 2.5 for a definition of the marker position) to the PPP engine by using the
command.
Automatic Seeding:
the receiver can be configured to automatically seed the PPP engine
from its current DPGS or RTK position. Automatic seeding is configured with the
command.
2.4.4.2
PPP Datum Offset
By default, PPP positions are expressed in ITRS (which ITRF realization of ITRS depends on
the PPP service provider), while RTK positions refer to the regional datum used by your RTK
provider. To avoid coordinate jumps each time the PVT engine switches between RTK and
PPP, and to ensure accurate seeding of the PPP engine from RTK, the regional datum must
be provided with the
command.
Note that local RTK positions obtained after applying the datum transformation parameters
transmitted in RTCM v3.x MT1021-1023 are never used for PPP seeding. In other words,
the position reported in the
SBF block is not suitable for PPP seeding. See also
section 2.4.6.
2.4.4.3
Tide Corrections
Since PPP is based on global satellite corrections, the PPP position would be sensitive to earth
tide variations if no correction were applied. The receiver applies a tide correction based on
the Sinko Earth tide model
. All positions reported in the
and
SBF blocks are always tide-corrected.
2.4.5
Transition between PVT Modes
Whenever possible, the transitions from a more accurate PVT mode to a less accurate PVT
mode are smooth. For example, when switching from RTK to DGPS mode, the position does
not exhibit a sudden jump, but slowly degrades from RTK to DGPS accuracy.
(2)
Sinko, J., A Compact Earth Tides Algorithm for WADGPS. Proceedings of ION GPS-95, Palm Springs, California,
September 12-15, 1995, pp. 35-44.
64
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Страница 147: ...3 Command Line Reference PVTMode Static StandAlone SBAS DGPS RTKFloat RTKFixed Cartesian1 COM1 147 ...
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