Tradition and Virtuality: The Caltagirone Staircase

Computer Graphics (CG) and Virtual Reality (VR) are two of the most interesting research fields in Computer Science. In this paper we present an application of CG and VR in arts, tourist promotion and cultural heritage. We propose a technique able to simulate the Saint Mary of the Mount staircase, a magnificent staircase in Caltagirone, a beautiful baroque town in Sicily (Italy). Our system is an example of how new technologies may lead to a new way of interacting with traditional arts. Caltagirone and the Staircase Hill of vases, Queen of mountains, City of the ceramics: these are some of the names by which Caltagirone is remembered, whose name derives from the Arab Qal’ at Alghiran that means “castle of vases”. The element of greater tourist interest of the city is the Saint Mary of the Mount staircase. The staircase was realized in the 1606 by the architect Giuseppe Giacolone with a set of 150 steps. The entire structure was remade in the 1843 by the architect Salvatore Marino who reduced the number of steps to 142. They exceed an unevenness of approximately 50 meters and are large 7 meters. The staircase becomes protagonist when, in religious or civil festivity occasions, a spectacular manifestation is represented. The perpendicular disposition of the steps allows the composition of motifs that in remote times were only geometrics. Such motifs were obtained with paper goblets, white, red or green, that, oily lighted, diffused a faint light rendering a suggestive effect along the steps. The Proposed Algorithm Experimental Results Tradition and Virtuality: The Caltagirone Staircase Valentina Campisi, Gianpiero Di Blasi, Giovanni Gallo [email protected], [email protected], [email protected] D.M.I. University of Catania Via A. Doria, 6 – 95125 Catania – Italy IPLab@CT http://www.dmi.unict.it/~iplab/ An on line demo can be found at the following web address: www.dmi.unict.it/~gdiblasi/caltagirone/caltagirone.html Conclusions & Future Works In this paper, we presented a technique to simulate the Caltagirone staircase. This work can be viewed as a proof of concept to demonstrate how CG and VR can be useful in the field of arts and tourist promotion. Future work will be addressed to the extension of our method to other kind of arts and to the creation of a framework for the rapid development of virtual worlds for arts. Half-Toning Half-toning is a process that simulates shades of gray by varying the size of tiny black dots arranged in a regular pattern. This technique is used in printers, as well as the publishing industry. Digital half-toning is similar to half-toning in which an image is decomposed into a grid of halftone cells. In our method we adapt the Error Diffusion technique in order to select colors in the set {red, green, dark white, black}. This simple algorithm allows to reproduce a color image using only four colors (the traditional goblets colors available). Perspective Correction When an object is seen from a great distance it endures a perspective deformation due to the distance from the object itself. If, given an image, it is brutally “painted” on the staircase the obtained result is a figure remarkably lengthened in the closer part and remarkably narrow in the farther part. The artists who plan the staircase know these problems and (manually) correct the error due to the perspective deformation. Our algorithm performs the same operation applying to the original (half-toned) image a “perspective anti-deformation”, which lengthens the farther part and shortens the closer part, in such a way that when the image is visualized on the staircase the perspective deformation “will correct” the adhoc created artificial error. The 3D Model The heart of any VR application is the 3D model representing the virtual scene. In our case the 3D model is relatively complex (in number of elements), but it is very easy to construct. There are three fundamental elements in our scene: the staircase, the steps and the goblets. The staircase is only a container object, in particular it contains 142 steps. The steps are simple rectangular boxes containing everyone about 40 goblets. Goblets are opportunely colored cylinders. Level of Detail To light the staircase over 4000 goblets are used. It could be very prohibitive to manage in a virtual environment such amount of cylinders: it is necessary to “deceive” the viewer. The cylinders in the far steps are small, so they can be substituted by a box opportunely colored. Using this simple but smart trick it is possible to improve the performance of the algorithm and consequently the responsiveness of the system, making the user experience more pleasing. This simple technique is usually called LoD (Level of Detail), in particular we use a Distance-LoD, that is a level of detail driven by the distance from the viewer: as the distance increases less details can be used and vice-versa.