3D MODELS OF PHLEGRAEAN AREA (NAPLES) FOR GIS APPLICATIONS

Cira Oliviero, Claudio Parente, Daniela Pennacchio, Raffaele Santamaria

Dipartimento di Scienze Applicate, Università degli Studi di Napoli “Parthenope”, Via De Gasperi n. 5, 80133 Napoli [email protected], [email protected], [email protected], [email protected]

Phlegraen Area is a volcanic region in Campania (South of Italy), along the Parthenopean Gulf (Tyrrhenian Sea) between Bagnoli and Cuma (Province of Naples). This very fertile and sunny land, with a mild climate and natural sheltered ports, includes Mediterranean ecosystems, mosaics of habitats, ancient oak forests as well as craters, lakes and submerged roman relics. GISs (Geographical Information Systems) can be fundamental instruments for sustainable development of this area, but maps plain representations are inadequate for applications environmental aspects because of their limitations for correct spatial analysis. In this paper the procedures adopted to obtain 3d models of Phlegrean Area are illustrated. Cartographic data in vector format and Gauss-Boaga (Transverse of Mercator) representation (scale 1:5.000), referred to local (Italian) datum named Roma40, are used to build a TIN (Triangulated Irregular Network) and a DEM (Digital Elevation Model).

INTRODUCTION

Phlegraen Area was among the first sites settled by the ancient Greeks on the Italian peninsula. In Roman times, Cumae, Baiae, and Puteoli (Pozzuoli) became very prosperous cities and fashionable watering places. Some of the approximately 30 craters that are present in this region still emit sulphurous vapours and mineral waters. In Phlegraen area is Monte Nuovo (123 m), the youngest mountain in Europe, created by an eruption during one week in 1583. Another particular place is Lago Averno, a crater lake which is said to be the entrance to Hell because it turns blood red during particular times of the year as a result of the volcanically induced algal blooms. Interesting natural resource is Astroni Crater, a primeval place where an enchanted forest is conserved. The whole area is included in Province of Naples.

CARTOGRAPHIC DATA

Data used to build 3d models are derived from digital (vector) maps, named “elements”, produced by Province of Naples in scale 1:5.000. The cartographic representation is Gauss-Boaga and datum Roma40: plan metric coordinates (latitude and longitude) are referred to the international ellipsoid oriented at Monte Mario (Rome); the area is included in the second zone, named “East zone”; false origin valueto produce positive East plane coordinates is 2.520.000 meters; heights are referred to sea level. The main characteristics of datum and representation adopted in these maps are resumed in the table of figure 1.

Ellipsoid Hayford (international) a=6.378.388 m f=1/297 orientated at Monte Mario (Roma), =41° 55' 25.51" =0° (12° 27' 08.400" East Greenwich); azimuth on Monte Soratte: =6° 35' 00.88".

Representation Gauss-Boaga; Italian territory is included in two zone (West and East Zone), each of 6° in longitude; Central Meridian (longitude from Monte Mario): -3° 27' 08.400" (West Zone); 2° 32' 51.600" (East Zone); False origin for East coordinates: 1500 Km (West Zone); 2520 Km (East Zone); Scale Factor: 0.9996.

Figure 1: The main characteristics of datum and representation used in the digital maps considered for 3d-models construction

Using software ArcGis 8.1 (ESRI), queries have been generated (SQL, Structure Query Language) to select only contour lines and spot heights. Comparison between original and derived files is evidenced in figure 2.

TIN CONSTRUCTION

TIN (Triangular, or Triangulated, Irregular Network) is a form of the tesseral model based on triangles, which vertices form irregularly spaced nodes. It is built from joining points, each of them is defined by x,y,z coordinates, with edges to form a set of non-overlapping triangles used to represent the surface. TIN is also called irregular triangular surface model or irregular triangular mesh. In figure 2 the triangulation generated with 3d-Analyst, extension of ArcGIS, using the mentioned maps data, is presented; in figure 3 the whole model produced with the same software is enhanced by different colours for different level classes; in figure 4 a 3d visualization produced with ArcScene, other extension to navigate and explore models, is proposed .

Figure 2: Particular of TIN triangulation

Figure 3: TIN of Phlegrean area built with 3d Analist (ArcGis 8.1, ESRI)

Figure 4: 3d view of TIN in ArcScene (ArcGIS 8.1, ESRI), particular of Astroni Crater

DEM CONSTRUCTION

DEM (Digital Elevation Model) is computer representation of the earth's surface based on a grid: it consists of a sampled array of elevations for a number of ground positions at regularly spaced intervals that are referenced to some geographical coordinate system (latitude-longitude or plane coordinates). The files can be in either ASCII or binary. Softwares can generate DEM from dataset of points irregularly distributed using an interpolation method (such as: inverse weighed distance, natural neighbors, kriging). Using the same data for TIN generation, DEM of Phlegrean Area has been built with kriging method. The vertices of TIN have been converted in .txt file which has been elaborated with Surfer 8 (Golden Software): the model has been generate considering 20 m x 20 m cell size and interpolating the heights of no less than 32 and no more than 64 points for each grid node. The whole model is represented in figure 5.

Figure 5: 3d view of DEM built with Surfer 8 (Golden Software)

CONCLUSIONS

TIN as well as DEM accuracy is less than accuracy of similar model that can be generated using other data, such as the results of laser-scanning survey, airphotos, satellite high resolution images. However the models described in this paper supply interesting instruments to be used in many cases, such as volcanic studies and environmental impact assesment. TIN and DEM, infact, are fundamental for calculation of areas and Volumes as well as for classification of zones in reference to illumination, wind exposition and so on. Considering the accuracy of the maps and the procedures adopted for 3d models generation, TIN and DEM obtained can became the base for many GIS applications concerning the Phlegrean area.

REFERENCES

Jones, C. (1997), Geographical Information System and Computer Cartography, Longman Press, London Maguire, D. J., Goodchild, M. F., Rhind, D. W. (1991), Geographical Information Systems: principles and applications, Longman Press, London Burrough, P.A., McDonnell, R.A., (2000), Principles of Geographical Information Systems, Oxford University Press, Oxford 2000 ArcGIS 8.1 (ESRI) User Guide (2000) Surfer 8 (Golden Software) User Guide (2002)

BRIEF OF BIOGRAPHIES OF THE AUTHORS

Cira Oliviero is graduaded in “Environmental Sciences” at University of Naples “Parthenope”. At present she is a PhD student (Doctorate in Geodetic and Topographic Sciences) at he same University and conduct studies on reconstruction of shoreline evolution originated by erosion phenomena. She is also involved in a research project on web-GIS construction.

Claudio Parente is researcher at University of Naples “Parthenope”. Graduated in “Civil Engineering” at University of Naples “Federico II”, he obtained Phd in “Geodetic and Topographic Sciences” in 1999 (thesis on “Digital Cartography and GIS”). Author of several publications on different aspects of survey and representation, he is involved in national and regional projects on Cartography and GIS applications.

Daniela Pennacchio obtained PhD in “Geodetic and Topographic Sciences” at University of Naples “Parthenope” (thesis on “Use of satellite high resolution images for updating maps”). Graduated in “Environmental Sciences” at the same University, she is author of some publications on GIS applications, satellite images elaboration and digital cartography.

Raffaele Santamaria is Professor of Navigation and Cartography at University of Naples “Parthenope”. Graduated in Nautical Sciences, he coordinated several projects on GPS, Cartography and GIS applications. Author of many publications on scientific review, he presented the results of his activities at national and international meetings, conferences and workshops.