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

Single-frequency receivers as master permanent stations in GNSS networks: precision and accuracy of the positioning in mixed networks

The use of GPS/GNSS instruments is a common practice in the world at both a commercial and academic research level. Since last ten years, Continuous Operating Reference Stations (CORSs) networks were born in order to achieve the possibility to extend a precise positioning more than 15 km far from the master station. In this context, the Geomatics Research Group of DIATI at the Politecnico di Torino has carried out several experiments in order to evaluate the achievable precision obtainable with different GNSS receivers (geodetic and mass-market) and antennas if a CORSs network is considered. This work starts from the research above described, in particular focusing the attention on the usefulness of single frequency permanent stations in order to thicken the existing CORSs, especially for monitoring purposes. Two different types of CORSs network are available today in Italy: the first one is the so called “regional network” and the second one is the “national network”, where the mean inter-station distances are about 25/30 and 50/70 km respectively. These distances are useful for many applications (e.g. mobile mapping) if geodetic instruments are considered but become less useful if mass-market instruments are used or if the inter-station distance between master and rover increases. In this context, some innovative GNSS networks were developed and tested, analyzing the performance of rover’s positioning in terms of quality, accuracy and reliability both in real-time and post-processing approach. The use of single frequency GNSS receivers leads to have some limits, especially due to a limited baseline length, the possibility to obtain a correct fixing of the phase ambiguity for the network and to fix the phase ambiguity correctly also for the rover. These factors play a crucial role in order to reach a positioning with a good level of accuracy (as centimetric o better) in a short time and with an high reliability. The goal of this work is to investigate about the real effect and how is the contribute of L1 mass-market permanent stations to the CORSs Network both for geodetic and low-cost receivers; in particular is described how the use of the network products which are generated by the network (in real-time and post-processing) can improve the accuracy and precision of a rover 5, 10 and 15 km far from the nearest station. Some tests have been carried out considering different types of receivers (geodetic and mass market) and antennas (patch and geodetic). The tests have been conducted considering several positioning approaches (static, stop and go and real time) in order to make the analysis more complete. Good and interesting results were obtained: the followed approach will be useful for many types of applications (landslides monitoring, traffic control), especially where the inter-station distances of GNSS permanent station are greater than 30 km

WEIGHTED ICP POINT CLOUDS REGISTRATION BY SEGMENTATION BASED ON EIGENFEATURES CLUSTERING

Abstract. Dense point clouds can be nowadays considered the main product of UAV (Unmanned Aerial Vehicle) photogrammetric processing and clouds registration is still a key aspect in case of blocks acquired apart. In the paper some overlapping datasets, acquired with a multispectral Parrot Sequoia camera above some rice fields, are analysed in a single block approach. Since the sensors is equipped with a navigation-grade sensor, the georeferencing information is affected by large errors and the so obtained dense point clouds are significantly far apart: to register them the Iterative Closes Point (ICP) technique is applied. ICP convergence is fundamentally based on the correct selection of the points to be coupled, and the paper proposes an innovative procedure in which a double density points subset is selected in relation to terrain characteristics. This approach reduces the complexity of the calculation and avoids that flat terrain parts, where most of the original points, are de-facto overweighed. Starting from the original dense cloud, eigenfeatures are extracted for each point and clustering is then performed to group them in two classes connected to terrain geometry, flat terrain or not; two metrics are adopted and compared for k-means clustering, Euclidean and City Block. Segmentation results are evaluated visually and by comparison with manually performed classification; ICP are then performed and the quality of registration is assessed too. The presented results show how the proposed procedure seem capable to register clouds even far apart with a good overall accuracy

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

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

Assessment of positioning performances in Italy from GPS, BDS and GLONASS constellations

The use of multiple GNSS constellations has been beneficiary to positioning performances and reliability in recent times, especially in low cost mass-market setups. Along with GPS and GLONASS, GALILEO and BDS are the other two constellations aiming for global coverage. With ample research demonstrating the benefits of GALILEO in the European region, there has been a lack of study to demonstrate the performance of BDS in Europe, especially with mass-market GNSS receivers. This study makes a comparison of the performances between the combined GPS-GLONASS and GPS-BDS constellations in Europe with such receivers. Static open sky and kinematic urban environment tests are performed with two GNSS receivers as master and rover at short baselines and the RTK and double differenced post processed solutions are analyzed. The pros and cons of both the constellation choices is demonstrated in terms of fixed solution accuracies, percentage of false fixes, time to first fix for RTK and float solution accuracies for post processed measurements. Centimeter level accuracy is achieved in both constellations for static positioning with GPS-BDS combination having a slightly better performance in comparable conditions and smaller intervals. GPS-GLONASS performed slightly better for longer intervals due to the current inconsistent availability of BDS satellites. Even if the static tests have shown a better performance of GPS-BDS combination, the kinematic results show that there are no significant differences between the two tested configurations. Keywords: GNSS, BDS, GLONASS, NRTK positioning, Accurac

Filtering and Mapping Public Health Data with an Innovative Kriging Approach, Accounting for Single Observation Variance

AbstractThe main scope of the paper is performing appropriate kriging interpolation of the diabetes prevalence data coming from the Pavia (Italy) Local Health Care Agency (ASL). The original dataset is analyzed, the Bayesian regularization is evaluated, which is applied by other authors and finally prevalence data are simulated by means of random fields, in order to tune and evaluate kriging interpolation