Detailed road surface measures are nothing without accurate positoning data. The RPS Geolocation System adds accurate positioning and precise alignment information to your recorded data.
Our positioning system comprises three elements: a GPS, an Inertial Measurement Unit (IMU) and a wheel rotation sensor. The GPS system is designed to produce accurate location, but all GPS systems have periods of loss of signal and short term errors. To reduce these short terms errors, a 6 degrees of freedom IMU is used to measure rotations and accelerations. Finally the wheel encoder is used to assist measurement of distance and velocity.
A dual antenna GPS systems enables detection of vehicle rotation. Survey quality, dual frequency GPS systems are used. GPS errors can be corrected automatically either with PPP correction via NASA's servers, or if more accuracy is required a reference station measurement is used. CORS network data can also be used.
In general, there are three levels of accuracy for inertial measurement systems: MEMS (lowest accuracy), FOG (medium/high accuracy), and RLG (highest accuracy). Most pavement measurement systems use MEMSsystems. While they appear to be quite accurate, they do have significant measurement drift with temperature. The Ring Laser Gyro (RLG) systems we use as part of the RPS PaveScout technology has orders of magnitude less drift, resulting in higher stability and higher accuracy measurements.
RPS has dedicated significant development to accurately combine the IMU, encoder and GPS measurements. We do not use simple filtering methods, but use detailed solution finding methods, which allow optimisation of measurements both forwards and backwards in time. The final result is the best positioning system possible: a combination of quality hardware, matched with quality software.