Hardware Overview of High‑Precision Positioning and Orientation Systems

1. Background

High‑precision maps and high‑precision collection vehicles are common terms in the mapping and mobility fields. But what does "high‑precision" actually mean?

High‑precision refers to high‑accuracy positioning. A high‑precision map contains rich geographic data and coordinates with high accuracy. A high‑precision collection vehicle is a specialized vehicle that gathers data for such maps.

People often ask how high‑precision is achieved and what qualifies as high‑precision. Currently, the standard is not strictly defined, but generally a precision of **centimeter‑level or better** is considered high‑precision. The implementation relies mainly on various sensors, especially the high‑accuracy positioning and orientation system, which includes satellite positioning and inertial navigation.

This article introduces the hardware aspects of these systems and their practical applications.

2. Terminology

Positioning and Orientation System (POS) : A combination of inertial navigation and GNSS satellite navigation that provides high‑accuracy position and attitude measurements. It uses a satellite receiver to determine spatial position and an inertial measurement unit (IMU) to determine instantaneous attitude, fusing both via precise timing.

Inertial Navigation System (INS) : Often abbreviated as "inertial navigation", it is a navigation solution that uses gyroscopes and accelerometers to compute the vehicle’s velocity and position within a navigation coordinate frame.

IMU (Inertial Measurement Unit) : A device that measures three‑axis attitude angles (or angular rates) and acceleration. It is a core component of an INS.

GNSS : Global Navigation Satellite System, encompassing all satellite navigation systems such as GPS (USA), GLONASS (Russia), Galileo (EU), BeiDou (China), and augmentation systems like WAAS, EGNOS, MSAS.

Note: Internally we often refer to the positioning part simply as "inertial navigation", which actually includes the whole hardware‑software positioning system.

3. What a High‑Precision Positioning and Orientation System Consists Of

The system on a collection vehicle typically includes the following components:

Composition of the Positioning and Orientation System

Algorithm Process

The system consists of hardware, accompanying software, and algorithms. Many combination‑solving algorithms exist in the industry; this article focuses on the hardware perspective.

Low‑precision and high‑precision positioning systems have similar compositions; the difference lies in the sensor accuracy (IMU, GNSS).

4. Roles of Various Sensors

4.1 GNSS

GNSS (e.g., GPS, BeiDou) provides absolute coordinates without error accumulation but has a lower update rate (typically ≤10‑50 Hz). High‑precision GNSS modules support multiple frequencies (L1/L2/L5) and channels, offering centimeter‑level post‑processing accuracy.

Major GNSS receiver manufacturers include Trimble, Novatel, Leica, Topcon, as well as domestic vendors such as BeiDou Xintong, Huace, Zhonghaida, and Sinan.

4.2 IMU

The IMU is the core of high‑precision positioning. It typically consists of three accelerometers and three gyroscopes. Accelerometers measure linear acceleration on three axes; gyroscopes measure angular velocity. After processing, the IMU provides attitude and relative position.

IMU data are relative; they cannot provide absolute position, so they are combined with GNSS. IMU update rates can reach several hundred to 1 kHz.

IMU technology ranges from mechanical gyroscopes, laser gyroscopes, fiber‑optic gyroscopes, to MEMS gyroscopes. MEMS devices are low‑cost and mass‑produced, while high‑end laser or fiber gyros offer higher precision.

Accelerometers come in various types (quartz flexure, liquid‑float, MEMS) and sensing principles (piezoelectric, piezoresistive, capacitive). Capacitive accelerometers are the most common.

4.3 Odometer

Mounted on the wheel, an odometer uses a rotary encoder (or magnetic, Hall‑effect sensors) to measure linear travel, helping to suppress drift when GNSS signals are lost.

4.4 Augmentation & Auxiliary Methods

Techniques such as RTK, RTD, PPK, PPP, DGPS, and various SBAS are used. In practice, land‑based augmentation is more common than satellite‑based.

5. How Inertial Navigation Is Built

5.1 Gyroscopes

Gyroscopes measure angular velocity. Types include mechanical, laser, fiber‑optic, and MEMS gyros. Mechanical gyros are bulky and less accurate; laser gyros use the Sagnac effect; fiber‑optic gyros replace the laser cavity with fiber; MEMS gyros integrate micro‑mechanical structures with CMOS.

5.2 Accelerometers

Accelerometers measure acceleration vectors. Types are classified by material (quartz, liquid‑float, MEMS) and sensing element (piezoelectric, piezoresistive, capacitive, thermal, resonant).

6. Why Combine Navigation Sensors

Single‑sensor navigation cannot meet all performance requirements. GNSS provides absolute position with good long‑term stability but low update rate; IMU offers high‑rate relative motion with good short‑term stability but drifts over time. Combining them leverages their complementary strengths.

7. Key IMU Parameters

Important specifications include:

8. Error Sources Affecting Accuracy

Major error sources are shown below:

Gyroscope factors : Bias, bias stability, random walk, temperature sensitivity.

Accelerometer factors : Stability and precision.

Temperature : Affects both gyroscope and accelerometer performance.

Error handling : Systematic errors (bias, scale factor, installation) can be calibrated; random errors (noise) are mitigated using Allan variance analysis or Kalman filtering.

9. How to Choose a Positioning System

Selection criteria include sensor performance, price, supply chain, integration difficulty, and vendor support. The primary focus is on meeting technical specifications.

9.1 Indicator Analysis

Key indicators for gyroscopes:

Range (e.g., ≤300 °/s for automotive)

Bias and bias stability (°/h, °/s)

Angle random walk

Physical considerations:

Form factor and mounting orientation

Power supply (9‑16 V typical for vehicles) and protection features

Interface types (USB, Ethernet, serial)

Environmental requirements (temperature, waterproofing, IP rating)

Relevant standards (GB/T 19392‑2013, ISO 16750, ISO 26262, GB/T 28046)

9.2 Emphasis on Testing

Practical testing is essential. Example devices:

Testing methods include real‑motion trials, software simulation, and hardware‑in‑the‑loop (HIL) semi‑physical simulation. Real‑motion trials (e.g., test‑car runs) provide the most direct accuracy assessment.

Typical test workflow:

Device preparation (install IMU firmly, ensure antenna visibility, provide power and data connections)

Route planning (cover diverse scenarios: highways, urban streets, tunnels, parking lots)

Data acquisition (collect raw GNSS/INS data from both the test device and a high‑grade reference device)

Data analysis (post‑process with differential correction, filter, fuse, and compare trajectories)

10. Conclusion

This article provides a hardware‑focused overview of inertial navigation devices and their sensors within positioning and orientation systems. Practical deployment also involves environmental testing, aging, screening, turn‑table calibration, and sophisticated sensor‑fusion algorithms to achieve high‑precision performance.

For readers interested in positioning and inertial navigation, the series of books by Prof. Qin Yongyuan and Prof. Yan Gongmin from Northwestern Polytechnical University are recommended.