1,720,980 research outputs found
Realizzazione di una rete GPS statica e cinematica: confronto con altre determinazioni
No full textA local GPS network has been established. All the points overlap cadastrial fisucial points of the Regione Autonoma Trentino Alto-Adige. The study area is in the surrounding of the Trento city, only three points are visible from each other and have been surveyed using traditional techniques. The GPS network has been inserted into the cartographic reference system computing the transformation parameters for the planimetric coordinates, while the orthometric heights have been obtained referring to the Italian geoid ITALGEO 95 provided by IGeS
Planning GPS automatico con ostruzioni realistiche
No full textA good planning is a key factor for the success of a GPS survey. A realistic forecast of the DOP requires to take into account the obstacles that can hide part of the sky. This is specially true in a mountaneous region (natural obstacle) and in the urban area (artifact obstacle). In practice it is relatively easy to take into account the various obstacle in the planning of a static survey, but it is more difficoult to do the same for a kinematic survey. In the present work an authomatic procedure for the planning of a kinematic survey has been realized with a dedicated procedure inside a GIS. The realized procedure is interfaced with the almanac, a DHM for the planning in M.A. and a carthographic data base for the planning in urban areas (still in project) and computes the DOP with the standard algorithm for the points in a given trajectory
Field measurements in river embankments: validation and management with spatial database and webGIS
No full textThis study focuses on the development of a system with a spatial database and a webGIS able to store, validate and display the data to assist the decision makers in managing Early Warning Systems for river embankment failure. In order to prevent misleading results it is essential to have a tool able of managing a large number of data for checking their reliability and for locating them in the space. In this paper, special attention was paid in the development of procedures to assess the reliability of the measures. For this purpose the database includes all the information needed to describe the instrument performance, such as the sand pack size and casing diameter of open-standpipe piezometers for evaluating their time lag, and the calibration curves of transducers with the possibility of their updating. The position of the non-functioning instruments is identified through the analysis of the electrical signal and spatial displays, while the analyses of the redundancy and coherence of measures is used for detecting doubtful data. Database and webGIS was applied to the monitoring data of an embankment of the Adige River in Northern Italy. The database and webGIS system has proved to be a suitable and effective tool for the management and validation of real-time data and periodical field measurements
GIS applications with GRASS
No full textThe application of GIS has become fundamental in environmental studies since it allows the integration of heterogeneous data.
Several applications of the GRASS GIS where the use of different data types leads to the realization of environmental models are presented.
The GRASS GIS has been used to develop and test forest fire risk models combining several morphologic, vegetational and anthropic factors; it has been used to set up a new avalanche risk model which allows the evaluation of the ability of the different vegetation types to protect against avalanches. A procedure for the automatic determination of the forest coverage evolution has been developed using the GRASS image analysis capability. The production of GPS satellites' visibility maps has been automated using the shadow generation algorithm in GRASS. This algorithm is also used to evaluate solar radiation and its relation to vegetation types
Hazard evaluation supported by spatial database and web-GIS
No full textThe real-time evaluation of hazard associated to natural or man-made phenomena requires the management of geospatial and temporal data, most of them collected by using automatic monitoring systems. If a theoretical model for interpretation has been defined, these data are first used to validate and calibrate the model, and then to identify the areas influenced by the hazardous phenomena and for predicting their evolution. In order to prevent misleading results it is therefore essential to have a tool able of managing a large number of data for checking their reliability and for locating them in the space. This study focuses on the development of a spatial database and a web-GIS able to storage, validate and display the data to assist the decision makers in managing an Early Warning Systems (EWS). By developing a Sensor Observation Service (SOS) the database could be linked to the sensors (including geospatial data and manual measures), and the web-GIS could interact with users for displaying the data and collecting more additional information.
The database was set up by using PostgreSQL and Post GIS; the web-GIS displays the time series of data through graphs made with Open Flash Charts.
Special attention was paid in the development of procedures to assess the reliability of the measures. For this purpose the database includes all the information needed to describe the instrument performance, such as the sand pack size and casing diameter of open-standpipe piezometers for evaluating their time lag, and the calibration curves of transducers with the possibility of their updating. The position of the non-functioning instruments is identified through the analysis of the electrical signal and spatial displays, while the analyses of the redundancy and coherence of measures is used for detecting doubtful data.
Database and web-GIS was applied to the monitoring data of an embankment of the Adige River in Northern Italy. Measures of groundwater pressure, soil vertical displacements, soil and instrument temperature, meteorology and water level of the river were processed. To date the monitoring system has been used to support the research activities, and the database and the web-GIS has facilitated the analysis and data sharing
Posizionamento GPS di un motoaliante attrezzato per misure in bassa atmosfera
No full textSi riporta un'esperienza di rilievo cinematico con tecnica GPS per lo studio delle circolazioni atmosferiche in ambiente vallivo. Si analizzano le diverse problematiche a partire dall'installazione della strumentazione di misura fino all'analisi critica dei risultati ottenuti, con particolare riferimento agli effetti di multipath indotti dall'aereo, agli effetti troposferici ed agli effetti delle variazioni dei centri di fase delle antenne
Nuovi sviluppi per la pianificazione di rilievi GPS cinematici terrestri o aerei
No full textA new approach for the planning of GPS campaigns, either static or kinematic, has been developed for the automatic determination of occlusions to the GPS signal due to natural or artifact obstacles. For each pixel of a raster map the maximum elevation of the obstacles depicted by a Digital Terrain Model is obtained in a polar diagram of the sky obstructions for each pixel of the map. Coupling this information with the satellite positions, given by the almanac file, it is possible to build satellites’ visibility maps.
This is fundamental for areas where obstructions are determinant for the satellite-receiver inter visibility, such as mountain areas or city centers.
The software is already suited for the integration within a GIS. The main reason behind this work is the need of planning the airborne surveys for environmental and meteorological studies organized by the Civil and Environmental Engineering Department of the University of Trento.
It is possible to create maps of satellites’ visibility for the whole area (static survey) or for a trajectory (kinematic survey), either on the DTM surface (ground vehicles) or fully three-dimensional (airborne vehicles)
A Web Processing Service for GNSS realistic planning
No full textThe spread presence of GNSS Permanent Station Networks makes satellite surveys simpler, quicker and cheaper, and the achievement of high precisions easier. However, the result of a GNSS campaign benefits from an accurate planning, especially in presence of natural or artificial obstructions that make satellite observations difficult. Most of the GNSS office suites provide planning tools to analyse the satellite's visibility; visibility plots, sky plots and DOP charts are commonly built from the GNSS almanac. They usually allow planning on single points, taking into account the obstructions due to terrain morphology or buildings by hand-drawing polar diagrams after a visit of each location to be surveyed. This task can be made fully automatic by using a digital surface model to build the obstruction plot and the almanac to evaluate satellites' positions, hence their visibility, in a GIS. The procedure may be applied to whole areas to find the best time for the survey campaign.
Taking a step further, this approach has been made available as a service by creating a Web Processing Service, which allows also non GIS specialists to access this tool through a simple webgis interface.
The user can select the satellites constellation, GPS and/or GLONASS, the cut-off elevation angle, the day, hour and temporal window of the survey. The service returns raster maps describing the minimum number of visible satellites and the PDOP index in every pixel. Moreover, the service implements some features of the UNAVCO TEQC software, which can help to choose the location of new permanent stations.
The implementation follows the OGC specifications and relies fully on FOSS software, combining different systems to provide the user web interface, the data storage and the processing engine.
The service features, the underlying technology and some examples will be presented in this paper
A Web Processing Service for GNSS realistic planning.
No full textThe spread presence of GNSS Permanent Station Networks makes satellite surveys simpler, quicker and cheaper, and the achievement of high precisions easier. However, the result of a GNSS campaign benefits from an accurate planning, especially in presence of natural or artificial obstructions that make satellite observations difficult. Most of the GNSS office suites provide planning tools to analyze the satellite's visibility; visibility plots, sky plots and DOP charts are commonly built from the GNSS almanac. They usually allow planning on single points, taking into account the obstructions due to terrain morphology or buildings by hand-drawing polar diagrams after a visit of each location to be surveyed. This task can be made fully automatic by using a digital surface model to build the obstruction plot and the almanac to evaluate satellites' positions, hence their visibility and not only availability, in a GIS. The procedure may be applied to whole areas to find the best time for the survey campaign. Taking a step further, this approach has been made available as a service by creating a Web Processing Service, which allows also non GIS specialists to access this tool through a simple WebGIS interface. The user can select the satellites constellation, GPS or GPS and GLONASS, the cut-off elevation angle, the day, hour and temporal window of the survey. The service returns raster maps describing the minimum number of visible satellites and the maximum PDOP index in every pixel for the temporal window. Moreover, the service implements some features of the UNAVCO TEQC software, which can help to choose the location of new permanent stations. The implementation follows the OGC specifications and relies fully on FOSS software, combining different systems to provide the user web interface, the data storage and the processing engine. The service features, the underlying technology and some examples will be presented in this paper
Valutazione tramite fotogrammetria e GIS della dinamica della copertura forestale e della provvigione legnosa
No full textIn the higher part of many Italian alpine regions the population is rapidly decreasing. This fact
directly influences landscape and forest management criteria. In particular, large pastures and
agricultured areas are being covered by trees or bushes, which change the landscape. This is a
well known trend but it is very difficult to evaluate the extension and the evolution of these
phenomena. A new approach to this problem has been developed at the Laboratorio Ambiente e
Territorio, which makes possible to determine changes of the forested areas over time. Series of
aerial photographs taken in different years (1954, 1980, 1994) have been compared using
automatic algorithms which exploit the GRASS GIS (Grass GIS is a public domain Geographic
Information System) image analysis capability. This method has proved to be effective for the
automatic determination of the widening of the forested areas. A precise knowledge of the forest
coverage evolution is very precious to enhance forest and landscape management criteria. It can
also be combined with demographic information to better explain landscape change.
Further investigations have been carried out to provide a photgrammetric tecnique for the
determination of the growing stock. Such tecnique has already been set up in the ’50 and in the
’60 using ad hoc photogrammetric surveys with mean scale of 1:10.000 and 1:20.000 for flat
areas and plantations. In this work an effort has been made to apply these technique to sparse
forests of spruce and larch in mountain areas using panchromatic images with mean scale
1:40.000. Measurements on the images of the single trees have been checked against the data
from forest management plans for the Trentino region
- …
