SX BLUE GPS iSXblue II+ GNSSTM, Руководство пользователя

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SXblue Series User Manual 69
SXblue receiver uses standard (RTCM 2.x and RTCM 3.x) and proprietary (ROX,
CMR, CMR+) real-time correction messages to achieve cm-level RTK.
In very simple words here are the various version of RTCM SC-104 and their
usage:
•
RTCM 2.0 - Pseudorange corrections for GPS L1 C/A code only. Usually
used for sub meter positioning.
•
RTCM 2.1 – Added GPS-only L1 carrier phase message to v2.0 for single
frequency RTK.
•
RTCM 2.2 – Equivalent to 2.0 with the addition of the GLONASS
pseudorange corrections.
•
RTCM 2.3 – Equivalent to 2.1 with single frequency carrier phase
corrections for both GPS and GLONASS.
•
RTCM 3.1 – Sends dual-frequency corrections for both GPS and GLONASS
for the highest level of performance for RTK work.
Note - RTCM is a local area data standard. This means that when positioning
with external correction, performance will degrade as a function of distance
from the base station. The additional degradation will depend on the
difference in observed orbit and ionospheric errors between the reference
station and the remote unit. This error is often seen as a bias in positioning,
resulting in a position offset. The scatter of the receiver is likely to remain
close to constant. RTK Networks overcome the limitations of relatively short
baseline length (distance between rover and base) with sophisticated
interpolation techniques.
SBAS (WAAS, EGNOS, MSAS, GAGAN) use a different correction format called
RTCA. When using SBAS (and $JMODE,BASE is set to “NO”, see chapter 5) The
RTCM SC-104 data output by the SXblue is converted from the RTCA SC-159
data broadcast by the SBAS networks. Appendix C - Resources contains the
contact information should you wish to purchase a copy of the RTCM SC-104
specification.
3.2 Configuring the SXblue Receiver
The SXblue receiver features three bi-directional ports (except SXblue 12/24 volts)
referred to as Bluetooth (Port A), Serial (Port B) and USB (Port C). GPS data
messages for all ports are easily configured by sending NMEA commands to the
SXblue receiver through either of its communication ports (the output of the Serial
Port can be configured through the Bluetooth port for instance and vice versa). The
$JASC NMEA message discussed in detail in the Technical Reference Manual