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gx/ix processing: improved accuracy in urban environments

Software Releases March 7, 2013

The latest software release from OxTS sees the launch of gx/ix processing, an exciting new technology that makes it possible to achieve better accuracy in urban environments and increase the accuracy of the RT2500 and RT2502 up to 40 per cent. Gx/ix processing is actually two standalone technologies (gx and ix), that are available in real-time and post-process. The correct one is selected automatically depending on the quality of GPS signals being received, and the system can switch between gx/ix as conditions dictate. It supports pseudo-range differential corrections and is compatible with forwards/backwards processing.

Gx initially appeared in late 2011, although it has been significantly enhanced with pseudo-range differential processing in the latest release. The real-time system accepts differential corrections in RTCMv3 format, and post-processing accepts RINEX as well. The gx mode uses raw GPS data and OxTS’ processing algorithms to calculate the GPS position and velocity, specifically tailored for use by our Kalman Filter. The solution computed by the GPS card is ignored and replaced by the gx solution. The GPS card’s solutions are not removed from logging, and the user can re-configure the system in post-process to recover the standard behaviour. Alternatively, gx/ix can be applied in post-process only. The gx solution can be combined far more confidently with the inertial data because gx processing selects and uses only the high-accuracy GPS satellite measurements. Significant improvements are especially visible in RT2500 and RT2502, which provides a low-cost, high-accuracy solution for customers.

Ix processing, also known as single satellite aiding, is a completely new and very exciting technology from OxTS, which complements gx capability and applies to all RT models (except those using Omnistar based receivers – RT3040/3050). The Kalman filter has been significantly enhanced to receive raw GPS measurements rather than GPS solutions (position/velocity). An initialised RT in ix mode doesn’t compute GPS position or velocity; it simply uses the information from any satellite it can see to adjust and maintain its position, whereas, a GPS solution (computed by the GPS card, or by the gx algorithm) requires at least four valid GPS satellite measurements. Therefore ix mode reduces drift and maintains navigation in challenging environments. Providing more integration between the GPS measurements and the inertial data, ix processing also detects and removes errors in single satellite measurements more effectively than gx. The RT system arbitrates between the gx mode and ix mode, switching between them based on the quality of the GPS measurements. Like gx, ix supports pseudo-range differential corrections and is compatible with forwards/backwards processing.

The strength of RT products has always been their ability to seamlessly blend inertial and GPS data in a way that cancels out the weakness of each standalone technology. The introduction of gx/ix technology, and the benefits it brings, is a good example of how inertial and GPS measurements can be leveraged to create a highly accurate and reliable platform customers know they can trust.

For more information on OxTS products, or to enquire about specific requirements, please contact OxTS or your national OxTS representative.

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