Miniature GNSS/INS

Miniature GNSS/INS for weight constrained applications.

The xNAV family combines GNSS technology with high-performance miniature inertial sensors to deliver a complete navigation solution in a lightweight package.

An IMU (Inertial Motion Unit) made of 3-axis accelerometer/gyroscope provides very accurate heading, roll, pitch, speed, heave and position.  Before making an evaluation of the X-NAV family of products by OXTS, a UK-based manufacturer of inertial navigation technology, we must take a step back and put things in perspective as far as the criteria by which one can make an evaluation of products of this type. We see that there are 3 categories of IMU:

• The high end – heavy – expensive IMU – Some types of IMU are very bulky, heavy and extremely expensive. They can be considered as reliable navigation devices even without aiding from a GNSS positioning system and are often used to navigate submarines or objects into space. Unfortunately, because they cost a fortune, and since they are very large and extremely heavy to carry these are not suitable for several types of application.
• The survey grade IMU – Some lighter and smaller versions are quite precise and work very well as a tool for carrying out precision surveys, but they are still expensive, yet not small and are accurately reliable without GNSS position aiding for a limited time (a matter of seconds). These types of IMU are commonly used in survey applications which primarily rely on satellite navigation. These devices come in hand in case of absence of satellite reception (dead reckoning) which generally occurs inside tunnels, under bridges and in urban areas.
• The solution for weight restricted application– The optimal solution comes from another type of inertial navigation sensors. Since the introduction of Micro-Electro-Mechanical Systems (MEMS), the size of a decent IMU has been enormously reduced a matter of centimetres, their weight to a few hundred grams and their price to around a few thousand euros. They are less precise but still excellent since they are constantly aided by satellite navigation.

The xNAV family of inertial navigation systems from OxTS combine GNSS technology with high-performance miniature inertial sensors to deliver a complete navigation solution in a lightweight package.

This product family finds applications in:

• Aerial photogrammetry
• Urban terrain mapping
• Disaster site monitoring
• LIDAR scanning
• Antenna tracking
• Camera stabilization
• UAV/UAS navigation
• Avionics

The key features are:

• Low weight xNAV systems use compact MEMS sensors to be as economical as possible, both in terms of price and power. But thanks to sophisticated calibration techniques and advanced embedded algorithms, the systems deliver exceptional performance in a surprisingly small package from just 365 g including rugged anodized aluminum enclosure. By seamlessly blending the inertial and GNSS data, the xNAV provides smooth, robust outputs even in poor GNSS environments.
• All in one box: The family comes with four different models delivering excellent value in terms of price vs. performance with antennas and software included for free. All models come with two input for a dual GPS antenna which provides stable heading performance in all conditions. Tactical grade IMU for 0.05° roll/pitch accuracy. Technology for tight coupling and inertial relock to maintain performance in harsh GNSS environments. Ethernet and Serial ports. Data is provided in output between 100 and 250 times per second and can be stored inside internal memory storage of 4GB.

The product family types are:

• xNAV200 &xNAV500 (dim: 132 x 77 x 36 mm; weight365gr,) with an embedded GNSS receiver GPS/GLONASS L1 which provided a precision of position of 0,5m.
• xNAV250 &xNAV550 (dim: 132 x 77 x 41 mm; weight425gr,) with an embedded survey grade GNSS – L1/L2 RTK receiver GPS/GLONASS which provided a precision of position of 2cm.

Integrating the xNAV into systems like UAVs couldn’t be simpler. Mounting brackets are supplied to ensure a rigid installation. Standard NMEA messages, timing sync and trigger outputs as well as event input triggers. These products can be used with an array of sensors such as LiDAR scanners, cameras, and hyperspectral sensors. OEM board set are available with attractive bulk discounts.

Summary

In summary, the xNAV systems use compact MEMS sensors to be as economical as possible, both in terms of price and power. Despite this constraint, by fusing the inertial and GNSS data, the xNAV provides smooth, robust outputs even in poor GNSS environments delivering exceptional performance in a small package.