Mass-Market Receiver for Static Positioning: Tests and Statistical Analyses

Nowadays, there are several low cost GPS receivers able to provide both pseudorange and carrier phase measurements in the L1band, that allow to have good realtime performances in outdoor condition. The present paper describes a set of dedicated tests in order to evaluate the positioning accuracy in static conditions. The quality of the pseudorange and the carrier phase measurements let hope for interesting results. The use of such kind of receiver could be extended to a large number of professional applications, like engineering fields: survey, georeferencing, monitoring, cadastral mapping and cadastral road. In this work, the receivers performance is verified considering a single frequency solution trying to fix the phase ambiguity, when possible. Different solutions are defined: code, float and fix solutions. In order to solve the phase ambiguities different methods are considered. Each test performed is statistically analyzed, highlighting the effects of different factors on precision and accurac

MONITORING OF LANDSLIDES WITH MASS MARKET GPS: AN ALTERNATIVE LOW COST SOLUTION

The territory of Italy is seriously afflicted by hydrological risk, with 82% of its area affected by this phenomenon. In recent years, technologies and advanced research have played an important role in realizing complex automatic systems devoted to landslide monitoring and to alerting the population. Sometimes, the cost of these systems (communications network, sensors, software, technologies) prevents their use, and in particular the cost of sensors has a large impact on the final investment. For example, geodetic GNSS receivers are usually employed to conduct landslide monitoring, but they are costly. Nowadays, new technologies make it possible to use small and efficient low cost single frequency GPS receivers, which are able to achieve a centimetrical or better level of accuracy, in static positioning. The rapid development and diffusion of the GNSS network to provide a positioning service has made it possible to use single frequency receivers, thanks to the use of virtual RINEX. This product is generated by a network of permanent stations. In this research, the actual performance of a mass market GPS receiver was tested, with the purpose of verifying if these sensors can be used for landslide monitoring. A special slide was realized, in order to conduct a dedicated test of the detection of displacements. Tests were carried out considering two factors: acquisition time and distance from the Virtual Station. The accuracy and precision of movement determination were evaluated and compared, for each test, considering the different factors. The tests and results are described in this contributio

Stand-Alone Satellite-Based Global Positioning

Stand-alone positioning is the first crucial step in the different types of GPS positioning. It is normally adopted only for pseudo-range measurements, after an ionospheric and tropospheric correction, estimated through calculated models. This positioning approach allows estimation of the position of the rover receiver in the ECEF (Earth Centred Earth Fixed) reference system, with a variable level of accuracy which depends on the number of satellites used, but generally it has a metrical level. Stand-alone positioning using pseudo-range measurements will be analysed in this chapter, starting from the actual measurements of a rover receiver. In this chapter, pseudo-range equations will be written and the balance between measurement equations and unknowns (positions and clock offsets) will be analysed. Equations of observation will be linearized in order to be able to solve the problem with the least squares approach, beginning by writing the design matrix. In least squares, it is important to use an adequate stochastic model, in particular some solutions with different weight matrices will be considered. The relative motion defined during the time of signal propagation due to terrestrial rotation and satellite motion is also considered. The iterative procedure devoted to correct the rover position from these effects will also be considered. The least squares solution is followed by the definition of the precision positioning, by means of the estimation of the variance–covariance matrix. Following the theoretical section, a calculus example is proposed, with the purpose of leading the reader to understand the practical positioning problem and to realize an autonomous calculus, verifying the achieved results. Error estimation is not considered here, referring the reader to another chapter. The Dilution of Precision (DOP) is another related topic described in this chapter. This index represents the geometrical quality of satellite constellations. It allows us to foresee the precision of stand-alone positioning, in order to plan the measures. It is derived from the equations regarding stand-alone positioning, where satellite positions are known through the Keplerian elements of the almanac. An example of DOP estimation and visibility of the GPS satellite will be included in this chapter

Il posizionamento satellitare: prospettive nel campo della geomatica con ricevitori GNSS basso costo

Sono passati circa vent'anni dalle prime esperienze GPS e solo guardando indietro nel tempo si può capire il cammino fatto nella tecnologia e nelle possibilità di misura dei nuovi ricevitori, alla luce delle nuove costellazioni e dei servizi di posizionamento a terra. Il GPS ha modificato non solo il modo di fare misure ma anche alcuni concetti ben saldi nella cultura del topografo. Vengono così ampliate le casistiche degli schemi di misura, gli approcci di calcolo, l'istituzione di reti geodetiche e il mantenimento dei sistemi di riferimento. Anche la cadenza di calcolo delle reti deve tener conto delle altissime precisioni raggiungibili e delle elevate frequenze con cui possono essere eseguite le misure e calcolate le posizioni. Tanti di questi concetti e tecniche fanno oggi parte della pratica professionale ma la ricerca non è finita. Miglioramenti tecnologici e scientifici aprono nuovi scenari e dunque occorre analizzare le nuove possibilità nel campo della geomatica. Uno degli aspetti sicuramente importanti di questi anni è il posizionamento con sensori a basso costo, che permettono il raggiungimento di precisioni interessanti in molti campi della geomatica e dell'ingegneria. Alcuni di questi permettono di effettuare un posizionamento indoor o con bassissime intensità di segnale oltre a poter registrare le misure sulla frequenza L1 per la post elaborazione. La potenziale grande diffusione conduce ad approfondire e sperimentare le prestazioni di tali ricevitori. Nella nota, verrà fatto un breve excursus storico e verranno proposti i risultati di alcune esperienze eseguite in ambiente outdoor e indoor in varie modalità di acquisizione ed elaborazion

Le reti NRTK alla luce del nuovo formato RTCM3

Le tecniche RTK richiedono formati di trasmissione dati: RTCM è attualmente lo standard indipendente dai formati proprietari dei ricevitori. Le versioni RTCM2.x stentano però a contenere le informazione necessarie per lavorare con reti RTK secondo i nuovi approcci basati sul principio Master Auxiliary per cui è stata rilasciata la versione RTCM3 nel 2004. In questa nota si spiegano le novità inerenti a questi formati e i loro recenti aggiornamenti, alla luce dello stato dell'arte delle reti RT

Recovery of cadastral boundaries with GNSS equipment

The purpose of this work is to propose a new redefinition of cadastral boundaries using GNSS equipment and cadastral maps. These maps are the ‘original' maps of the Italian Land Cadastre, the first cartographic support built directly from measures carried out by technicians during implantation of the Italian land cadastre. They are called ‘originali di impianto' - ‘originals of implantation' or ‘implant maps'. As such, these maps are valuable and are kept with great care. Recently, the Italian cadastre has carried out an accurate digitisation of these maps in a raster format at a high resolution. In this work, the authors propose the use of these digital maps for the recovery of cadastral boundary. The original cadastral map, one of the primary sources relied upon in defining legal boundaries, generally uses the Bessel ellipsoid localised in Genova and the Cassini-Soldner projection; the GNSS equipment, on the other hand, uses the geocentric ellipsoid with global or continental realisations. After an RTK positioning, the receivers usually provide the cartographic coordinates in a Gauss projection. However, our study deals with the problem of using different projections and reference systems within the limits of a map. In this context, the transition between systems and projections can be made through a conformal transformation with deformations slighter than graphical errors in the map. The difficulty of finding identifiable points in both reference systems is partially solved through a new way of carrying out the redefinition of boundaries by exploiting geometric informatio

Improving GNSS Landslide Monitoring with the Use of Low-Cost MEMS Accelerometers

Observation and monitoring of landslides and infrastructure is a very important basis for land planning, human activities, and safety. Geomatic techniques for deformation monitoring have usually involved GNSS and total station measurements or, more generally, expensive geodetic instruments, but other techniques, such as SAR (Synthetic Aperture Radar), can be efficiently applied. Using low-cost sensors could be an interesting alternative solution if the accuracy requirements can be satisfied. This paper shows the results obtained for tilt measurements using MEMS accelerometers, which were combined with mass-market GNSS sensors for monitoring five sites located on landslides. The use of a MEMS-like inclinometer requires an important calibration process to remove bias and improve the solution’s accuracy. In this paper, we explain the MEMS calibration procedure employed, with a simple and cheap solution. The results indicate that with a simple calibration, it is possible to improve measurement accuracy by one order of magnitude, reaching an angular accuracy of a few hundredths of a degree, verified by an independent technique

Colombia y Venezuela: desempeño económico, tipo de cambio y relaciones Estado-empresarios

En 1980, el ingreso per cápita venezolano en dólares era 1,4 veces mayor que el colombiano, pero en 2007 esta relación se invirtió y el ingreso colombiano fue 1,1 veces mayor que el venezolano. Un resultado que merece una explicación pues ambos países hicieron reformas estructurales similares para liberar la economía e integrarse a los mercados internacionales. Este trabajo intenta explicar ese resultado. La principal conclusión es que las relaciones Estado-empresarios y el manejo del tipo de cambio real son fundamentales para explicar la diferencia en el desempeño económico de ambos países

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 Flächen 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 exampl