The demand for high-definition surveys within cultural heritage-related projects represents one of the main factors that promoted the use of laser scanning technology and photogrammetry. By measuring millions of points within relatively short time periods, terrestrial laser scanners (TLS) allows to researchers to derive complete and very detailed three-dimensional (3D) models of real objects from acquired point clouds. These features drew in recent years the interest of surveyors, engineers, architects, and archaeologists towards the laser scanning technique as an invaluable surveying tool for 3D modeling of sites and artifacts of cultural heritage. A wide variety of objects, such as small pieces of pottery, statues, buildings, and large areas of archaeological sites, have been scanned and modeled for various purposes like preservation, reconstruction, study, and museum exhibitions. However, the use of TLS systems for stability control is still a research field not much investigated. In the view of in-depth investigation on this topic, a 3-years project has been established to evaluate the use of multiple surveying techniques for the stability control of a complex historical structure. To this aim, TLS, total station (TS) and photogrammetry are being employed for stability control monitoring with finite element model (FEM) analysis applied to an historical building, Teatro Olimpico (Olympic Theatre), in Vicenza, Italy. The main goal of this work is to analyze and verify the stability over time of this kind of structure by applying FEM analysis to a highly detailed 3D model of the theater. To date, three consecutive surveys of the theater have been carried out with consumer digital-reflex camera Nikon D200, a Leica Laser Scanner (HDS 3000) and a Leica Total Station (TCR 705). The first survey comprised approximately 250 pictures to derive a global and complete 3D model of theater with an inexpensive measuring and modeling photogrammetry software (Photomodeler). In the second study, the historical structure was fully surveyed with a TLS, the Leica HDS 3000, to produce a complete 3D model. A set of scans of complex elements, such as the wood trompe l'oeil onstage scenery, statues, and fine trim, were acquired in this stage. This article presents the results from the repeated surveys and highlights the issues and difficulties related to the laser scanning and photogrammetry of an unusual and complex geometry such as the one provided by the Olympic Theater in Vicenza.

Photogrammetry has dealt since many years with the 3D reconstruction of objects from images. It provides for accurate sensor calibration and object modeling using analog or digital imageries, it is very portable and many commercial software is available for image processing and 3D modeling. On the other hand, laser scanning technology and all the related reverse engineering software are becoming a very promising alternative for many kind of surveying and modeling applications. Laser scanners allow to acquire very quickly a huge amount of 3D data which can be often combined with color high-resolution digital images. Among the plenty of works so far presented, in particular on the use of laser scanning for cultural heritage survey, some modeling and accuracy related issues have been not yet solved and discussed in details. In this contribution we report about two case studies realized with photogrammetry and laser scanner and we provide some advices and suggestions about the more suitable 3D modeling method for a given object, taking into account its size and shape complexity, the required accuracy and the target application.