SMART7 Installation and Operation User Manual v6
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Chapter 4 SMART7 with SPAN Operation
NovAtel's Synchronous Position, Attitude and Navigation (SPAN
®
) technology brings together two very different
but complementary positioning and navigation systems namely Global Navigation 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:
l
NovAtel GNSS receiver
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 supports the timing require-
ments of the IMU and runs the real-time INS filter.
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IMU
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.
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GNSS antenna
In the SMART7-S and SMART7-SI, 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 configuration com-
mands 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 positioning can be accurate to within a few centimeters. If however, some or all of the
satellite signals 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 measured by accelerometers in three
perpendicular axes within the IMU and the gyros measure angular 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 initial 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 para-
meters 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, velocity 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 using the high accuracy GNSS
solution, the IMU errors can be modeled and mitigated. Conversely, the continuity and relative accuracy of the
INS solution enables faster GNSS signal reacquisition and RTK solution convergence.
The advantages of using SPAN technology are its ability to:
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Provide a full attitude solution (roll, pitch and azimuth)
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Provide continuous solution output (in situations when a GNSS-only solution is impossible)
