Smart7 With Span Operation; Fundamentals Of Gnss+Ins - Novatel SMART7 Installation And Operation Manual

SMART7 with SPAN Operation

NovAtel's Synchronous Position, Attitude and Navigation (SPAN
two very different but complementary positioning and navigation systems namely Global Nav-
igation Satellite System (GNSS) and an Inertial Navigation System (INS). By combining the best
aspects of GNSS and INS into one system, SPAN technology is able to offer a solution that is
more accurate and reliable than either GNSS or INS could provide alone. The combined
GNSS+INS solution has the advantage of the absolute accuracy available from GNSS and the
continuity of INS through traditionally difficult GNSS conditions.
A SPAN system consists of the following components:
NovAtel GNSS receiver
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The NovAtel OEM7 GNSS receiver uses a combination of GPS, GLONASS, Galileo, BeiDou,
NavIC and QZSS signals to calculate an accurate GNSS position. The OEM7 receiver also sup-
ports the timing requirements of the IMU and runs the real-time INS filter.
IMU
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The Inertial Measurement Unit (IMU) consists of three accelerometers and three gyroscopes
(gyros) so that accelerations along specific axes and angular rotations can be measured.
GNSS antenna
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In the SMART7-S, all of three of these components are included in the SMART7 enclosure. After
the SMART7 is installed, the appropriate power supply is attached, and a few simple con-
figuration commands are entered, the SPAN system will be ready to navigate.

4.1 Fundamentals of GNSS+INS

GNSS positioning observes range measurements from orbiting GNSS satellites. From these
observations, the receiver can compute position and velocity with high accuracy. NovAtel GNSS
positioning systems are highly accurate positioning tools. However, GNSS in general has some
restrictions which limit its usefulness in some situations. GNSS positioning requires line of sight
view to at least four satellites simultaneously. If these criteria are met, differential GNSS pos-
itioning can be accurate to within a few centimetres. If however, some or all of the satellite sig-
nals are blocked, the accuracy of the position reported by GNSS degrades substantially, or may
not be available at all.
In general, an INS uses forces and rotations measured by an IMU to calculate position, velocity
and attitude. This capability is embedded in the firmware of OEM7 receivers. Forces are meas-
ured by accelerometers in three perpendicular axes within the IMU and the gyros measure angu-
lar rotation rates around those axes. Over short periods of time, inertial navigation gives very
accurate acceleration, velocity and attitude output. The INS must have prior knowledge of its ini-
tial position, initial velocity, initial attitude, Earth rotation rate and gravity field. Since the IMU
measures changes in orientation and acceleration, the INS determines changes in position and
attitude, but initial values for these parameters must be provided from an external source. Once
these parameters are known, an INS is capable of providing an autonomous solution with no
external inputs. However, because of errors in the IMU measurements that accumulate over
time, an inertial-only solution degrades with time unless external updates such as position, velo-
city or attitude are supplied.
The SPAN system's combined GNSS+INS solution integrates the raw inertial measurements
with all available GNSS information to provide the optimum solution possible in any situation. By
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®
) technology brings together
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