Spherical photogrammetry for cultural heritage—San Galgano Abbey and the Roman Theater, Sabratha

Abstract

In this article, we present the results of the photogrammetric surveys of two important monuments, the Roman Theatre in Sabratha, Libya, and San Galgano Abbey, in Italy. The surveys were performed with a new photogrammetric technique, Spherical Photogrammetry, developed by Gabriele Fangi [2007, 2008, 2009, 2010]. The method is based on so-called spherical panoramas. These are obtained by stitching together several pictures taken from the same point and covering 360°, which are then mapped in a plane with an equi-rectangular projection. This technique is normally used to produce QuickTime movies which have already proven to be very useful for the documentation of cultural heritage. One panorama can replace many normal photographic images. Ease, rapidity, low cost, and completeness of the documentation are the main advantages of this technique. The Abbey of San Galgano is an important example of Gothic architecture in Italy. The church is empty and without its roof, which fell towards the end of the 18 th century. The photogrammetric survey was done in November 2009. Thirty-four panoramas were taken outside, around the perimeter of the complex, and 22 were taken inside the church. The Roman theatre of Sabratha, built in the 2 nd century AD, was rebuilt in the years between 1930-1940 at the command of the Italian governor of Libya, Italo Balbo, as a rememberance of the past Roman Empire. The project was handled by two Italian archaeologists Caputo [1953] and Guidi [1935]. The photogrammetric survey was done in August 2009 with 22 panoramas taken around and inside the monument. These two projects are limited in their scope, not covering the geometry of the entire monuments. The time and the available resources did not permit a complete survey. The purpose of the two projects was not to satisfy the needs of a client, but only to demonstrate the feasibility and the efficiency of the approach. In these two projects accuracy tests were not made, but in other projects accuracy was found to be on the order of 1/1000 the object distance, say one centimeter every ten meters of distance from the object [Fangi 2007a, 2007b, 2007c, 2009, 2010].