GNSS Heading

Key characteristics of GNSS heading

• True-north referenced: Aligned with true north, avoiding the drift and variations of magnetic north.
• Works while stationary: Provides absolute heading immediately, even when the machine is not moving.
• High accuracy: Achieves typical accuracy of 0.1° to 1.0° (depending on baseline length), provided high-quality, high-precision antennas are used.
• No magnetic interference issues: Completely unaffected by magnetic fields from motors, metal structures, or power lines.

What does heading mean? Understanding heading vs. other terms

Heading is the direction that the front of a vehicle or object is pointing. It’s measured in degrees, relative to true north.

Heading is related to but different from the following terms:

Term	Definition	Difference to heading
Course over ground (COG)	Direction of motion of a vehicle.	Heading is the way a vehicle is pointing, which may not be the direction it is moving. For example, a boat can be pointed toward the shore of a river but moving downstream, or heavy machinery can slide down a rocky hillside.
Roll	Rotation around the longitudinal, or front-to-back, axis.	Heading is a rotation around the vertical axis. Roll movement affects how upright the vehicle is.
Pitch	Rotation around the lateral, or side-to-side, axis.	Heading is a rotation around the vertical axis. Pitch movement affects whether the vehicle is pointing up or down.
Yaw	Rotation around the vertical, or top-to-bottom, axis.	Heading is essentially yaw that is aligned with true north. Yaw can be aligned with a different coordinate frame.
Attitude	A complete picture of a vehicle’s roll, pitch, and yaw.	Heading is one measurement of a vehicle’s orientation, not a complete picture.

How a GNSS heading system works

A GNSS heading system gives absolute heading, even when stationary, because it uses two GNSS antennas with a known, fixed distance between them (the so-called “baseline”). The system works in the following way:

• Signal acquisition: The system receives GNSS signals simultaneously at both antennas.
• Carrier-phase measurement: The system measures the phase difference of the satellite signals between the two antennas.
• Vector calculation: It computes a precise relative vector between the primary and secondary antennas.
• Heading output: By knowing the antennas’ fixed positions on the vehicle, the system calculates the angle relative to true north.

To put it simply, the system knows where the antennas are on the vehicle and the distance between them. By combining that data with the position measurements from each antenna, the system can determine the vehicle’s heading.

How to improve GNSS heading accuracy

There are several ways to optimize your GNSS heading measurements:

1. Ensure sufficient baseline length between antennas

   The antenna baseline, or distance between two antennas, is the single most important factor for heading accuracy. The baseline is inversely proportional to the error in the heading measurement, and the heading accuracy is a nonlinear function of baseline length. Simply put, the longer your baseline length, the better your heading accuracy is.

   Recommended baseline lengths

   To ensure a stable and high-performing heading, follow these baseline guidelines:

   • Optimal, ≥ 1 meter: Provides the best possible accuracy and system robustness. Recommended for heavy machinery, marine vessels, and large UAVs.
   • Standard, 50 cm – 1 meter: The recommended range for most high-precision commercial products. This provides a balance of compact design and reliable heading data.
   • Minimum threshold, 30 cm – 50 cm: While the system will function, accuracy and reliability begin to decrease significantly in this range.
   • Not recommended, < 30 cm: Baselines shorter than 30 cm are not recommended due to high error rates and reduced signal reliability.

   Pro tip: If your machine’s form factor allows, always aim for a baseline of at least 1 meter to maximize the performance of the carrier-phase calculations.

2. Choose the right antenna

   An antenna is a critical part of any GNSS system design. The choice and implementation of the antenna can ultimately play a significant role in overall GNSS performance.

   For a GNSS-based high-precision heading solution, where directional information is given based on carrier-phase measurements of two antennas, the importance of antenna selection is obvious. It is recommended to use two identical high-performance, high-precision, multi-band or all-band antennas, with ground planes, for robust, reliable heading information in real-world applications.

   Additionally, to minimize the effects of phase center variation on heading accuracy, the two antennas should be mounted with identical orientation.

3. Use all-band, all-constellation GNSS

   GNSS data is transmitted over different bands, and each band has different GNSS constellations available for positioning data. The more GNSS bands and the more GNSS constellations you are using, the better signal availability you can get, which contributes to better positioning accuracy even in a challenging environment. The more accurate carrier-phase measurement data you get from each antenna, the more accurate the heading information is.

Common use cases for GNSS heading

Precision agriculture

For the precision agriculture industry, auto-steering and lightbar guidance systems need precise heading information. GNSS heading provides precise orientation data, even when stationary, enabling more effective and safe operation.

Construction

The orientation of heavy machinery such as cranes and graders can be accurately measured using the GNSS heading vector.

UAVs

GNSS heading is a game-changer for unmanned aerial vehicles (UAVs). It provides accurate yaw data immune to motor interference and instant IMU alignment on the launch pad.

GNSS-based heading information is highly needed for applications such as agricultural and delivery UAVs.

Marine and robotics navigation

GNSS heading can be used for autopilot, radar alignment, and dynamic positioning of a ship.

GNSS heading vs. other heading methods

Method	Stationary heading	Susceptible to interference	Reference
Magnetic compass/magnetometer	Yes	High, metal and motors	Magnetic north, drifts over time
Gyro / IMU	No, drifts	Medium, vibration	Relative, local
GNSS heading	Yes	Low	True north, stable

Why it matters

GNSS heading is a highly reliable reference for automation. It offers stability near metal, immediate data without needing movement, and global reliability for autonomous navigation.