Feature Article Published by the IEEE Computer Society 0272-1716/04/$20.00 © 2004 IEEE IEEE Computer Graphics and Applications 21 M any cultural heritage applications require 3D reconstruction of real-world objects and scenes. Over the past few years, it has become increasingly common to use 3D digitization and modeling for this purpose. This is mainly due to advances in laser-scanning techniques, 3D modeling software, image-based modeling techniques, computer power, and virtual reality. Many approaches are cur- rently available. The most common are based on sur- veys and CAD tools and/or traditional photogrammetry with control points and a human operator. However, this approach is time-consuming and can be costly and impractical for large-scale sites. Modeling methods based on laser-scanned data and more automated image-based techniques have recently become avail- able. Our approach integrates several technologies based on our experience over more than a decade of trying to accurately and completely model large-scale heritage monuments and sites. Using both interactive and auto- matic techniques, we can model a highly detailed struc- ture or site at various levels of detail. We use image-based modeling for basic shape and structural elements, and laser scanning for fine details and sculpt- ed surfaces. To present the site in its proper context, we use image-based rendering for landscapes and sur- roundings. To apply this approach, we created hundreds of models from sites all over the world for documenta- tion, walk-through movies, and interactive visualiza- tion. The results were compelling and encouraging. Motivation and requirements There are many motives for 3D reconstruction of her- itage sites: ■ documenting historic buildings and objects for recon- struction or restoration in case of fire, earthquake, flood, war, erosion, and so on; ■ creating educational resources for history and culture students and researchers; ■ reconstructing historic monuments that no longer or only partially exist; ■ visualizing scenes from viewpoints impossible in the real world due to size or accessibility issues; ■ interacting with objects without risk of damage; and ■ providing virtual tourism and vir- tual museum exhibits. In general, most applications specify eight requirements: high geometric accuracy, capture of all details, photorealism, high automa- tion level, low cost, portability, application flexibility, and model size efficiency. The order of impor- tance of these requirements depends on the application’s objec- tive—for example, whether it’s for documentation or virtual tourism. A single system that can satisfy all eight requirements is still in the future. In particular, accurately capturing all details with a fully automated system for a wide range of objects and scenes remains elusive. For small and medium objects, up to the size of an average adult person, range-based techniques such as laser scanners can provide accurate and complete details with a high degree of automation. However, being rel- atively new systems that aren’t produced in large quan- tities, these scanners remain costly. They are also not portable enough for a single person to carry around and An integrated approach for selecting the most effective technique for modeling large-scale heritage sites combines several technologies to create accurate and complete models. Sabry F. El-Hakim, J.-Angelo Beraldin, Michel Picard, and Guy Godin National Research Council of Canada Detailed 3D Reconstruction of Large-Scale Heritage Sites with Integrated Techniques