Low cost mobile mapping systems: an Italian experience

Road cadastre mapping is a topic of current interest in Italy because each Region has to prepare one. The main problem is to obtain an accurate low cost product but in a brief operational time. Nowadays, many tools exist to solve this problem: one of these is the mobile mapping. Different integrated systems (GNSS, IMU, video camera) are available that allow accurate and quick mapping. These systems are usually expensive. Starting from some previous international experience, a low cost mobile mapping system has been developed that employs 2 GNSS receivers, 1 IMU, 1 digital video camera and some dedicated software tools to calibrate, manage and use the system. These devices have been installed on a particular crossbar, which was installed on the roof of a standard vehicle. This allows the images to be recorded using the video camera and single frames are directly georeferenced. This system must be first calibrated using a special control network; in this way, it is possible to use this platform on any vehicle and the system is completely independent of the support. The recorded videos are divided into single frames and each one is georeferencing using GNSS and IMU data. Moreover each frame is used to identify the single details on the road (i.e. traffic signal) which are the main components of the road cadastre map. It is then possible to reconstruct the roadway axis and the average between two trajectories. A special software devoted to defining each axis has been developed. The aim is to recover the position of the axis with submetric accuracy. A special algorithm has been used, which works considering the ortho distance between the axes. This system has been tested over several kilometres: accuracy of the shape, axes and roadways has been estimated, considering the limits imposed by Italian law about road cadastral mapping. The results obtained, in particular the accuracy of the relief, the quality and the calibration procedures are described in this paper. The main product of this work is that it is possible to obtain a low cost mobile mapping system (about 25 Keuro), with a good accuracy which is useful for any kind of vehicle.