Alberto Cina

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.

Augmented positioning with CORSs network services using GNSS mass-market receivers

Over the last twenty years, positioning with low cost GNSS sensors has become widespread worldwide at both commercial and academic level. The Geomatics Research Group of DIATI at the Politecnico di Torino has carried out several experiments in order to evaluate the precision achievable when using mass-market GNSS receivers with a network of permanent GNSS station (also called CORSs network - Continuous Operating Reference Stations) for various purposes. The aim of this study is to investigate real effect and the role of the CORSs Network for this type of receivers, and especially how the products generated by the CORSs network can be used to improve the level of accuracy and precision if mass-market receivers are considered. The rapid development and diffusion of the GNSS network which provides a positioning service has enabled us to use single frequency receivers both in post-processing and real time approach by means of virtual RINEX and differential corrections. In the first approach, in order to determine the possible level of accuracy and precision obtainable with this sensor, a special test field was carried out which enabled us to study the variation of position with millimetrical accuracy. Tests were carried out considering various types of receivers (geodetic and mass market) and antennas (patch and geodetic) in static mode. The static test was carried out by acquiring raw data for 24 hours and dividing them into small parts (5, 10 or 15 minutes each), in order to consider the effect of the acquisition time on the final results and also consider the complete constellation. The postprocessing was performed with a commercial software. An interesting advantage is the possibility of generating a VR close to the rover position especially when mass market sensors are used, with the aim of creating a short (few meters) baseline, or in extreme cases it is possible to realize a null baseline thus eliminating the bias with the double differences in a relative positioning. By using a VR we obtain an independent solution in respect to the master-rover distance in attempt of fixing the ambiguity phase. The real-time experience was carried out with mass-market receivers for NRTK (Network Real Time Kinematic) positioning within the Regione Piemonte CORSs network. Two network products were used (VRS® and nearest correction): RTKLIB software was used in order to apply these corrections to the raw data of the mass market receivers. Some very good results were obtained which are reported in this paper.

Network Real Time Kinematic (NRTK) Positioning - Description, Architectures and Performances

In this last years, the differential GNSS positioning has had an intensive expansion, especially due to the development and realization of GNSS CORSs (Continuous Operating Reference Stations) networks. One of the main goals of these networks is to give the possibility to the users to extend the differential positioning (whether in real time or post-processing) up to 25-50 km, allowing a positioning useful for applications such as surveying, monitoring and precise navigation. It is possible to find in bibliography some studies that shown the performances of this type of positioning, with their limitations and peculiarities, also in function of the network size. The Network Real Time Kinematic (NRTK) positioning is a very common practice not only in academia but also in the professional world. Since its appearance, over 10 years ago, a growing number of people use this type of positioning not only for topographic applications, but also for the control of vehicles fleets, precision agriculture, land monitoring, etc. This chapter wants try to focus the attention on the methods and characteristics of NRTK positioning and to summarize principles and peculiarities of this type of GNSS positioning: the goal is to show how networks for NRTK positioning work and also to show the differential corrections that are available today, with their performances in order to obtain acceptable results, always considering the accuracy required by the purposes described above. So, first of all the GNSS network positioning will be discussed, starting from the network biases estimation to the rover positioning with particular attention to the differential GNSS corrections such as the Master Auxiliary Concept (MAC), Virtual Reference Station (VRS) and Flachen Korrektur Parameter (FKP). Particular attention will be also devoted both to the transmission of the differential corrections and their problems, such as the GSM coverage, and to the analysis of the RTCM protocol. A theoretical description of the network calculation and biases interpolation will be made and brief results for each correction will be shown, in order to give a practical example