Vector Sensor Reference Manual 19
1.4.1 Moving Base Station RTK
The Vector Sensor’s internal GPS engines use both the L1 GPS C/A code and carrier phase data to
compute the location of the secondary GPS antenna in relation to the primary GPS antenna with a
very high sub-centimeter level of precision. The technique of computing the location of the
secondary GPS antenna with respect to the primary antenna, when the primary antenna is moving,
is often referred to as moving base station Real-Time Kinematic (or moving base station RTK).
RTK technology generally is very sophisticated and requires a significant number of possible
solutions to be analyzed where various combinations of integer numbers of L1 wavelengths to
each satellite intersect within a certain search volume. The integer number of wavelengths is often
referred to as the Ambiguity as they are initially ambiguous at the start of the RTK solution.
The Vector Sensor places a constraint on the RTK solution with the prior knowledge of the fact
that the secondary GPS antenna has a fixed separation of 0.50 m from the primary GPS antenna
on the bracket of the Antenna Array. This reduces the search volume considerably (and hence
startup times) since the location of the secondary antenna can theoretically fall only on the surface
of a sphere with radius 0.50 m centered on the location of the primary antenna (versus a normal
search volume that’s greater than a cubic meter).
1.4.2 Supplemental Sensors - Reduced Search Time
In addition to incorporating two internal GPS engines, integrated inside the Vector Sensor are a
gyro, magnetometer, and a tilt sensor. When used, the combination of the tilt sensor and the
magnetometer aid the rate at which a heading solution is computed on startup and also during
reacquisition if the GPS heading is lost due to obstructions. Each supplemental sensor may be
turned on or off individually, however, the full functionality of the Vector Sensor system is realized
only when each are used.
The tilt sensor reduces the search volume further beyond the volume associated with just a fixed
antenna separation, since the Vector Sensor knows the approximate inclination of the secondary
antenna with respect to the primary. The magnetic sensor is able to provide a general indication of
the true heading, reducing the search volume further. The gyro has a similar benefit as the
magnetic sensor, however only on reacquisition since it initially requires a GPS heading to self-
calibrate. The gyro is more accurate for the short term than the magnetic heading sensor and it
further reduces the search volume. Reducing the RTK search volume also has the benefit of
improving the reliability and accuracy of selecting the correct heading solution by eliminating other
possible, erroneous solutions.
Note - By default, the tilt aiding and gyro are turned on, however, the magnetic
sensor is turned off for shipping. The magnetic sensor should be turned on when
Vector Sensor is mounted in its final location.
1.4.3 Supplemental Sensors - Heading System Backup
The magnetic sensor and the gyro are able to operate as secondary sources of heading during
periods of GPS outage due to obstruction. We require that you turn on the magnetic aiding once
the installation is complete. You may configure the Vector Sensor to use the gyro aiding if you
choose. Since the gyro is more accurate than the magnetic sensor for short periods of outage, if
both sensors are used, the Vector Sensor will use the gyro for heading initially during an outage. If
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