588 research outputs found

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

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    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

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    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

    3D GIS BASED EVALUATION OF THE AVAILABLE SIGHT DISTANCE TO ASSESS SAFETY OF URBAN ROADS

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    The available sight distance (ASD) in front of the driver to detect possible conflicts with unexpected obstacles is fundamental for traffic safety. In the last 20 years, road design software (RDS) has been continuously updated with dedicated modules to estimate ASD, thus assessing the quality of project from a safety point of view. Unfortunately, the evaluation of ASD still represents an issue in the case of existing road, and the object of discussion in the research community. To avoid problems related to the limitation associated with the use of digital terrain models typically employed in RDS, the Geographic Information Systems (GIS) software can use digital surface models (DSM) which are more flexible in the modelling of sight obstruction due to vegetation, street furniture, and vertical surfaces largely diffused in urbanized areas. The paper deals with the evaluation of GIS in the estimation of ASD in a typical urban road where the density of sight obstruction along the roadside is relatively high. The work explores the case study of a collector road in the city of Turin (Italy). Results confirm the potentiality of GIS software in capturing the complex morphology of the urban environment, thus confirming that GIS could become an important analysis tool for road engineers in the field of road safety. The investigation here described is part of the Pro-VISION Project (funded in 2014 by the Regione Piemonte, Italy)

    Stand-Alone Satellite-Based Global Positioning

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    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

    Monitoring post-fire forest recovery using multi-temporal Digital Surface Models generated from different platforms

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    Wildfires can greatly affect forest dynamics. Given the alteration of fire regimes foreseen globally due to climate and land use changes, greater attention should be devoted to prevention and restoration activities. Concerning in particular post-fire restoration actions, it is fundamental, together with a better understanding of ecological processes resulting from the disturbance, to define techniques and protocols for long-term monitoring of burned areas. This paper presents the results of a study conducted within an area affected by a stand-replacing crown fire (Verrayes, Aosta (AO), Italy) in 2005, which is part of a long-term monitoring research on post-fire restoration dynamics. We performed a change detection analysis through a time sequence (2008-2015) of DSMs (Digital Surface Models) obtained from LiDAR (ALS - Airborne Laser Scanner) and digital images (UAV - Unmanned Aerial Vehicle flight) to test the ability of the systems (platform + sensor) to identify the ongoing processes. New technologies providing high-resolution information and new devices (i.e. UAV) able to acquire geographic data “on demand” demonstrated great potential for monitoring post disturbance recovery dynamics of vegetation

    Estimating the Available Sight Distance in the Urban Environment by GIS and Numerical Computing Codes

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    The available sight distance (ASD) is that part of the roadway ahead which is visible to the driver, and should be of sufficient length to allow a vehicle traveling at the designated speed to stop before reaching a stationary object in its path. It is fundamental in assessing road safety of a project or on an existing road section. Unfortunately, an accurate estimation of the available sight distance is still an issue on existing roads, above all due to the lack of information regarding the as-built condition of the infrastructure. Today, the geomatics field already offers different solutions for collecting 3D information about environments at different scales, integrating multiple sensors, but the main issue regarding existing mobile mapping systems (MMSs) is their high cost. The first part of this research focused on the use of a low-cost MMS as an alternative for obtaining 3D information about infrastructure. The obtained model can be exploited as input data of specific algorithms, both on a GIS platform and in a numerical computing environment to estimate ASD on a typical urban road. The aim of the investigation was to compare the performances of the two approaches used to evaluate the ASD, capturing the complex morphology of the urban environment

    Le reti NRTK alla luce del nuovo formato RTCM3

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    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

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

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    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 cosÏ 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

    A low cost mobile mapping system (LCMMS) for field data acquisition: a potential use to validate aerial/satellite building damage assessment

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    Among the major natural disasters that occurred in 2010, the Haiti earthquake was a real turning point concerning the availability, dissemination and licensing of a huge quantity of geospatial data. In a few days several map products based on the analysis of remotely sensed data-sets were delivered to users. This demonstrated the need for reliable methods to validate the increasing variety of open source data and remote sensing-derived products for crisis management, with the aim to correctly spatially reference and interconnect these data with other global digital archives. As far as building damage assessment is concerned, the need for accurate field data to overcome the limitations of both vertical and oblique view satellite and aerial images was evident. To cope with the aforementioned need, a newly developed Low-Cost Mobile Mapping System (LCMMS) was deployed in Port-au-Prince (Haiti) and tested during a five-day survey in FebruaryMarch 2010. The system allows for acquisition of movies and single georeferenced frames by means of a transportable device easily installable (or adaptable) to every type of vehicle. It is composed of four webcams with a total field of view of about 180 degrees and one Global Positioning System (GPS) receiver, with the main aim to rapidly cover large areas for effective usage in emergency situations. The main technical features of the LCMMS, the operational use in the field (and related issues) and a potential approach to be adopted for the validation of satellite/aerial building damage assessments are thoroughly described in the articl

    Specific alpine environment land cover classification methodology: Google Earth Engine processing for Sentinel-2 data

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    Land Cover (LC) plays a key role in many disciplines and its classification from optical imagery is one of the prevalent applications of remote sensing. Besides years of researches and innovation on LC, the classification of some areas of the World is still challenging due to environmental and climatic constraints, such as the one of the mountainous chains. In this contribution, we propose a specific methodology for the classification of the Land Cover in mountainous areas using Sentinel 2, 1C-level imagery. The classification considers some specific high-altitude mountainous classes: clustered bare soils that are particularly prone to erosion, glaciers, and solid-rocky areas. It consists of a pixel-based multi-epochs classification using random forest algorithm performed in Google Earth Engine (GEE). The study area is located in the western Alps between Italy and France and the analyzed dataset refers to 2017–2019 imagery captured in the summertime only. The dataset was pre-processed, enriched of derivative features (radiometric, histogram-based and textural). A workflow for the reduction of the computational effort for the classification, which includes correlation and importance analysis of input features, was developed. Each image of the dataset was separately classified using random forest classification algorithm and then aggregated each other by the most frequent pixel value. The results show the high impact of textural features in the separation of the mountainous-specific classes the overall accuracy of the final classification achieves 0.945
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