Overview

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Precision is a subjective word in the world of GNSS. For some applications, metre-level accuracy is “good enough”, even with the potential for errors and position jumps. Other applications require highly precise centimetre-level positioning that is reliable and available 24/7 over a wide area.

Whatever the desired accuracy, advances in GNSS correction services have greatly improved the availability and performance of positioning solutions. Sara Masterson, business development manager of correction services at NovAtel,
said, “The corrections industry overall is constantly evolving and improving the available correction service options in support of the user community, extending the range and types of conditions under which the service can be delivered.”

Back to Basics

Selection of the appropriate augmentation method or correction service depends on the performance required for each application. There are essentially four levels of positioning: standalone uncorrected; positioning derived from publicly available correction services such as the WAAS network in North America or Europe’s EGNOS system; positioning solutions derived from globally available subscription-based L-band services; and regional/ local RTK network solutions.

Standalone uncorrected and WAAS/EGNOS type solutions provide accuracies ranging from 1-10 metres. On the other end of the scale, RTK correction networks provide the most accurate centimetre-level solutions. While L-band solutions deliver corrections directly to the GNSS receiver via satellite, RTK solutions require a base station and a radio to get the corrections needed, limiting operator flexibility and increasing total system cost and complexity.

With subscription-based L-band correction services, users receive Precise Point Positioning (PPP) corrections to help mitigate and remove measurement errors and position jumps. PPP solutions utilize modeling and correction products including precise satellite clock and orbit data to enhance accuracy. Such services range in price from $300 to $4,000 per year, depending on the desired accuracy, end user application and subscription duration.