GNSS and IMU in Mobile Mapping: How They Work Together

IMUs and GNSS technology are important for mobile mapping. Find out how they differ and where they each excel.

This article was updated in 2026 to include the Meridian and Meridian Lite.

GNSS (Global Navigation Satellite System) determines absolute position using satellite signals. IMU (Inertial Measurement Unit) tracks orientation and movement using internal accelerometers and gyroscopes. In mobile mapping, the two are used together: GNSS provides accurate global coordinates, while the IMU fills in the gaps when satellite signals are lost or degraded – such as in tunnels, under tree cover, or in urban canyons. Together, they enable continuous, accurate georeferencing of every captured image and point cloud.

What is the difference between GNSS and IMU?

	GNSS	IMU
What it measures	Absolute position (latitude, longitude, altitude)	Relative movement (acceleration, angular velocity)
Signal source	External (satellites)	Internal (accelerometers, gyroscopes)
Works indoors?	No – requires line of sight to satellites	Yes – fully self-contained
Accuracy over time	No cumulative drift; variable with signal quality	Drifts over time without correction
Latency	Higher (satellite signal processing)	Very low (real-time sensor output)
Used alone in mapping?	Rarely – signal gaps cause errors	No – drift accumulates without GNSS correction
Best used	Establishing absolute position outdoors	Bridging GNSS gaps; measuring orientation and tilt
In Mosaic systems	Onboard GNSS fully integrated in all Mosaic systems	Integrated in Meridian, Meridian Lite, and Mosaic Xplor

IMU (Inertial Measurement Unit) and GNSS (Global Navigation Satellite System) are both navigation and mapping technologies. However, they have different purposes and functions.

IMUs are sensors that measure acceleration and angular velocity in order to determine the orientation and movement of a device. They use a combination of accelerometers, gyroscopes, and sometimes magnetometers to determine their orientation relative to the Earth.

GNSS, on the other hand, determines the location, velocity, and time of a receiver on the Earth’s surface with satellites. The most well-known GNSS system is the Global Positioning System (GPS), which is operated by the United States government.

In summary, IMUs provide information about the orientation and movement of a device, while GNSS provides information about the location of a device. Each technology has its own strengths and limitations. They can be used in combination to improve the accuracy and reliability of navigation and mapping systems.

When is it best to use IMU over GNSS?

The choice between using an IMU and/or GNSS depends on the specific needs and requirements of the application. Here are some scenarios where using an IMU might be more beneficial:

• Indoor or Enclosed Environments: GNSS signals can be disrupted or lost in indoor or enclosed environments, making IMUs a more reliable option for determining orientation and movement in these environments.
• Dynamic Environments: IMUs are often used in applications where the device is moving quickly or experiencing rapid changes in orientation, such as in robotics, drone navigation, or sports equipment. IMUs provide real-time information about orientation and movement, allowing the device to respond quickly to changes in the environment.
• High-Precision Orientation: For applications that require high-precision orientation information, IMUs can be a better option than GNSS. IMUs provide information about orientation and movement in real-time and can be combined with other technologies, such as Kalman filters, to improve their accuracy.

When is it best to use GNSS over IMU?

Here are some scenarios where using a GNSS might be more beneficial than using an IMU:

• Outdoor Environments: GNSS signals can be received in outdoor environments. GNSS is a reliable option for determining location, velocity, and time. It can provide location information with high accuracy, especially when multiple satellites are in view.
• Location-Based Services: GNSS is often used in applications that require location information, such as navigation systems, geolocation services, and mapping. GNSS provides real-time information about the location of a device, allowing these applications to function accurately.
• Large-Scale Mapping: For applications that require large-scale mapping, GNSS can provide a global reference frame. Now, maps can cover large areas with high accuracy.

Scenario	Best approach	Why
Outdoor open-sky mapping	GNSS + IMU	GNSS provides absolute position; IMU smooths trajectory
Tunnel or underground	IMU only (temporarily)	No satellite signal; IMU dead-reckons until signal returns
Indoor mapping	IMU + SLAM	No GNSS; SLAM builds a local map to localise within
High-vibration environments	High-grade IMU priority	Low-grade IMUs are unreliable under vibration
Large-area outdoor survey	GNSS-led with IMU assist	GNSS ensures global accuracy; IMU handles short outages
Fast-moving vehicle (>80 km/h)	Tightly coupled GNSS/IMU	Loose coupling introduces lag; tight coupling handles speed

Let’s break it down more and see what each of these is, and some of the companies behind these sensors. 

What is an IMU?

An IMU (Inertial Measurement Unit) is a sensor device that measures a body’s specific force, angular rate, and sometimes magnetic field. It combines accelerometers (which measure linear acceleration) and gyroscopes (which measure rotational velocity) to track the orientation and movement of a device in real time – without any external signals.

They typically consist of a combination of accelerometers, gyroscopes, and sometimes magnetometers.

How, where, and why are IMUs used?

IMUs have a wide range of applications. They are in basic navigation and orientation to more advanced applications such as robotics, drone navigation, and autonomous vehicles. 

Here are some examples of where IMUs are used:

• Smartphones: IMUs in smartphones provide motion tracking, orientation, and stability control.
• Drones: IMUs in drones provide precise control and stability during flight.
• Robotics: IMUs in robots provide real-time information about movement and orientation. They enable robots to navigate and perform tasks autonomously.
• Virtual Reality (VR) and Augmented Reality (AR) Head-Mounted Displays (HMDs): In VR and AR HMDs, IMUs track head and body movement. They enable users to interact with virtual environments in real-time.
• Wearables: IMUs in wearables track and monitor physical activity, including steps taken, calories burned, and sleep patterns.
• Automotive Systems: IMUs are in some advanced driver assistance systems (ADAS) in cars. They provide stability control and driver assistance.
• Industrial Equipment: IMUs are in industrial equipment such as cranes, excavators, and heavy machinery. They provide precise control and stability during operation.
• Mobile mapping units: They are also common in mobile mapping and surveying. They can provide precise and accurate location, orientation, and movement information.

What advantages can an IMU give the user?

One of the main advantages of using IMUs in mobile mapping is that they can provide accurate location and orientation information even in environments where GPS signals may be weak or unavailable. This is because IMUs rely on internal sensors rather than external signals to determine a device’s location and orientation. Additionally, IMUs can improve the accuracy and precision of data collected during mobile mapping surveys. This is because they can provide real-time corrections for errors caused by factors such as device tilt or movement.

What types of IMUs are there?

There are many different types and models of IMUs available on the market. They have varying levels of precision, accuracy, and features. Some basic IMUs may only provide basic information such as orientation and acceleration. However, more advanced IMUs may include features such as multi-axis measurement, temperature compensation, and built-in data logging.

In mobile mapping, there are many companies that specialize in providing IMU solutions, such as Applanix, NovAtel, and Trimble. These companies offer a range of IMU solutions for different applications and budgets. It’s worth comparing their products and features to determine which IMU solution would best suit your specific needs.

What are the key features of an IMU?

There are several key features that can make an IMU “good” or above average. Some of these include:

Precision and accuracy:

The precision and accuracy of an IMU’s measurements are one of the most important factors to consider. High-precision and accurate IMUs can provide more reliable and accurate data. This is critical for applications such as mobile mapping and navigation.

Multi-axis measurement:

An IMU with multi-axis measurement capabilities can provide information on multiple degrees of freedom, such as roll, pitch, and yaw. This can be useful for applications that require detailed information on the orientation of a device.

Temperature compensation:

Some IMUs include temperature compensation capabilities. They can help to ensure that measurements remain accurate over a wide range of temperatures.

Data logging:

Some IMUs include built-in data logging capabilities, which can be useful for recording measurements over an extended period of time.

Interfaces:

Different IMUs offer different interfaces to connect with other devices or systems, such as UART, I2C, USB, Ethernet, and so on. The availability of the interfaces will depend on the application that you have.

Robustness:

Some IMUs can withstand harsh environmental conditions, such as high vibrations, extreme temperatures, and humidity. This can be important for applications such as robotics and autonomous vehicles, where the IMU may be subject to harsh conditions.

Size and power consumption:

Some IMUs are compact and lightweight, which can be useful for applications such as drones and wearable devices. Additionally, the power consumption of an IMU can also be an important factor to consider, particularly for applications that require long battery life.

What is IMU drift, and why does it matter in mobile mapping?

Because IMUs calculate position by integrating acceleration over time, small measurement errors accumulate – a phenomenon called IMU drift. Over a few seconds, drift is negligible. Over minutes, it can introduce positional errors of several meters.

This is why IMUs in professional mobile mapping systems are always paired with GNSS: the satellite signal periodically resets the IMU’s reference position, keeping cumulative drift within acceptable bounds.

In Mosaic’s Meridian systems, a tightly coupled GNSS/IMU integration uses a Kalman filter to continuously fuse satellite and inertial data, minimizing drift even during extended GNSS outages – such as when driving through a tunnel or under a dense tree canopy.

What is GNSS? 

GNSS (Global Navigation Satellite System) is an umbrella term for any satellite-based navigation system that provides positioning, velocity, and time data to receivers anywhere on Earth. GPS (operated by the United States) is the most widely known GNSS system, but others include GLONASS (Russia), Galileo (Europe), and BeiDou (China). Modern mobile mapping receivers typically track multiple constellations simultaneously for improved accuracy and reliability.

How, where, and why are GNSS used?

GNSS devices are used in a wide range of applications, from basic navigation and location-based services to more advanced applications such as surveying, mapping, and autonomous vehicles. They can also be used in combination with other technologies, such as Inertial Measurement Units (IMUs), to improve their accuracy and reliability.

In mobile mapping, GNSS devices are used to determine the precise location and orientation of a mapping device as it moves through an environment. This information helps create accurate maps and survey data. It can also help correct for errors caused by factors such as device tilt or movement.

Image credit

GNSS (Global Navigation Satellite System) and GPS (Global Positioning System) are widely used in a variety of devices and applications. Here are some examples:

• Personal Navigation Devices: Handheld GPS units, smartphone navigation apps, and wearable GPS devices use GNSS/GPS for navigation and location tracking.
• Automotive Navigation: Many modern vehicles have built-in GNSS/GPS navigation systems, providing drivers with turn-by-turn directions and real-time traffic updates.
• Geographical Information Systems: GNSS/GPS is used in GIS (Geographical Information Systems) to collect, manage, and analyze geographic data, such as topographical maps, land use patterns, and environmental data.
• Surveying and Mapping: GNSS/GPS is important in surveying and mapping to determine precise location and elevation information, such as in the construction of roads, buildings, and infrastructure.
• Agriculture: GNSS/GPS is useful in agriculture for precise planting, harvesting, and soil analysis, as well as for monitoring livestock and wildlife.
• Drones: GNSS/GPS is used in drones for navigation, location tracking, and precise mapping of large areas.
• Search and Rescue: GNSS/GPS helps in search and rescue operations to locate individuals and track their movements in real-time.

What advantages can a GNSS give the user?

One of the main advantages of using GNSS devices in mobile mapping is their ability to provide precise location information on a global scale. Additionally, GNSS devices can help improve the speed and efficiency of mobile mapping surveys, as they can provide real-time location information without the need for additional equipment or manual measurements.

What types of GNSS are there?

There are many different types and models of GNSS devices available on the market, with varying levels of precision, accuracy, and features. Some basic GNSS devices may only support GPS, while more advanced GNSS devices may support multiple GNSS systems, such as GLONASS, Galileo, and BeiDou, which can improve the accuracy and reliability of location information.

In mobile mapping, there are many companies that specialize in providing GNSS solutions, such as Trimble, Leica, Geosystems, Carlton, and Topcon. These companies offer a range of GNSS solutions for different applications and budgets, and it’s worth comparing their products and features to determine which GNSS solution would best suit your specific needs.

What are the key features of a GNSS?

Here are some key features to look for when evaluating the quality of a GNSS (Global Navigation Satellite System) device:

• Multi-Constellation Support: A high-quality GNSS device should support multiple satellite constellations, such as GPS, GLONASS, Galileo, and BeiDou, to ensure the most accurate and reliable positioning information.
• High Update Rate: A high-quality GNSS device should have a high update rate, providing frequent and accurate location updates. This is especially important for applications that require real-time or near-real-time positioning information, such as autonomous vehicles or robotics.
• Wide Area Augmentation System (WAAS) Support: A GNSS device that supports WAAS improves the accuracy of positioning information in areas with limited or obstructed GPS signals.
• RTK Capability: Real-Time Kinematic (RTK) GNSS devices provide centimeter-level accuracy, making them a good choice for applications that require high-precision location information, such as surveying, mapping, and construction.
• Low Power Consumption: For applications that require long battery life, a GNSS device with low power consumption is important.
• Robust Design: A high-quality GNSS device should be robust and reliable, with features such as a rugged design and resistance to water, dust, and shock.
• Easy to Use: A GNSS device that is easy to use and has a user-friendly interface is important for applications where time is of the essence.
• Cost: High-quality GNSS devices can range in cost, with more advanced features typically resulting in a higher price point. It’s important to evaluate the specific needs and requirements of an application and choose a GNSS device that offers the best combination of features and cost.

*Other alternatives to GPS: VPS and CPS. 

What is GNSS accuracy, and what affects it?

Standard GNSS accuracy for a single-frequency receiver is typically 3–5 meters. For professional mobile mapping applications, this is insufficient. High-accuracy GNSS receivers used in systems like the Mosaic Meridian use RTK (Real-Time Kinematic) or PPK (Post-Processed Kinematic) corrections to achieve positional accuracy of 2–5 cm horizontally.

Accuracy is affected by: number of satellites in view, signal obstructions (buildings, trees, bridges), atmospheric conditions, and multipath errors (signals bouncing off surfaces before reaching the receiver). This is why GNSS alone is not sufficient for mobile mapping – the IMU compensates during periods of degraded signal.

How do GNSS and IMU work together in a mobile mapping system?

In a mobile mapping system, GNSS and IMU are not used independently – they are fused together through a process called sensor fusion, typically implemented using a Kalman filter. Here’s how the integration works in practice:

1. GNSS establishes absolute position. As the vehicle moves, the GNSS receiver continuously calculates its location relative to a global coordinate system, accurate to within centimeters when using RTK correction.

2. The IMU fills the gaps. When GNSS signals are interrupted – driving under a bridge, entering a tunnel, or moving through a dense urban canyon – the IMU takes over. Using the last known GNSS position as a starting point, it dead-reckons the vehicle’s movement using accelerometer and gyroscope data.

3. The Kalman filter continuously reconciles both. The filter weights GNSS and IMU data based on their current reliability, producing a smoother, more accurate position estimate than either sensor could provide alone. When GNSS resumes, it corrects any drift that accumulated during the outage.

4. The camera or LiDAR timestamps match the position. Every image frame and LiDAR point is tagged with a precise timestamp that maps to a fused GNSS/IMU position – ensuring accurate georeferencing of all captured data.

In the Mosaic Meridian and Meridian Lite, this GNSS/IMU fusion is tightly integrated at the hardware level, delivering positional accuracy sufficient for cadastral surveying, road asset management, and infrastructure inspection.

Frequently asked questions

What is the difference between GPS and GNSS?

GPS is one specific GNSS system, operated by the United States government. GNSS is the broader category that includes GPS plus other satellite systems: GLONASS (Russia), Galileo (European Union), and BeiDou (China). Modern professional receivers track all available constellations simultaneously, which improves accuracy and reduces the risk of signal gaps.

What is tightly coupled vs loosely coupled GNSS/IMU integration?

In loosely coupled integration, the GNSS receiver outputs a processed position which is then fused with IMU data. In tightly coupled integration, raw GNSS signals (pseudoranges) are fused directly with IMU data before any position solution is computed. Tightly coupled systems are more robust during partial GNSS outages – they can still function with fewer than 4 satellites in view, where loosely coupled systems would fail.

How accurate is GNSS/IMU positioning in mobile mapping?

With RTK-corrected GNSS and a tactical-grade IMU, modern mobile mapping systems achieve horizontal positional accuracy of 2–5 cm and vertical accuracy of 3–8 cm under good sky conditions. During GNSS outages, accuracy degrades depending on outage duration and IMU grade – typically remaining within 10–30 cm for outages under 5 seconds with a high-grade IMU.

Does Mosaic’s Meridian use GNSS and IMU?

Yes. The Mosaic Meridian and Meridian Lite both integrate a GNSS receiver and IMU as core positioning components, with tightly coupled sensor fusion for continuous, accurate georeferencing – including during tunnels, bridges, and other signal-degraded environments.

Mosaic Meridian as a solution

If you are looking for a mobile mapping camera solution that already includes or can integrate with any of the above devices, then you’re in the right place. Mosaic cameras come with a built-in GPS, allowing users to capture image data and geo-referenced points all at the same time and on one device. 

Our Meridian is a mobile mapping system that integrates the Mosaic X with a LiDAR system and GNSS receiver. This groundbreaking solution meets the needs of surveying, mapping, and GIS professionals who demand high-quality imagery and reliable LiDAR data.

The Meridian Lite is our more budget-friendly package. It features a Mosaic 51 camera and is ideal for urban environment data capture. The rolling shutter design captures the imagery you need today without overdoing it and clogging up the post-processing. Capture today and deliver results tomorrow!

Already have your own LiDAR unit? No worries! Mosaic cameras are also able to easily integrate with additional sensors, such as external GNSS, IMUs, wheel encoders, and LiDAR. So you can mix and match with the sensors that will give you the best data for your use case. 

Find out more about our cameras here. 

And when you’re ready to reach out, contact us here.