Eurographics Symposium on Rendering (2005) Kavita Bala, Philip Dutré (Editors) Out-of-Core Photon-Mapping for Large Buildings D. Fradin and D. Meneveaux and S. Horna SIC Laboratory, University of Poitiers, France † Abstract This paper describes a new scheme for computing out-of-core global illumination in complex indoor scenes using a photon-mapping approach. Our method makes use of a cells-and-portals representation of the environment for preserving memory coherence and storing rays or photons. We have successfully applied our method to various buildings, composed of up to one billion triangles. As shown in the results, our method requires only a few hundred megabytes of memory for tracing more than 1.6 billion photons in large buildings. Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture/Image Generation 1. Introduction Rendering massively complex environments remains a dif- ficult challenge to overcome. Though recent research have provided methods capable of rendering several hundred mil- lion triangles at interactive frame rates [ACW * 99, WDS04], global illumination techniques still remain difficult, due to computing time and memory management. For buildings, large occluders, such as walls, highly re- duce the number of objects seen from a given viewpoint or region. Global illumination techniques can benefit from this information, as shown in previous approaches for the radios- ity method [ARFPB90, TFFH94]. Usually, the scene is first subdivided using a binary space partitioning (BSP) decom- position [ARFPB90, TFFH94]. The resulting cells are sepa- rated by portals used to estimate a visibility graph and po- tentially visible sets (PVS). While PVS drastically reduce the initial number of polygons required for the computation, accurate estimation remains time-consuming and difficult to implement. Even with PVS, the information necessary to perform global illumination in a given region can easily ex- ceed the available memory for series of potentially visible rooms containing a high number of polygons. Christensen et al. [CB04] demonstrated that it is possi- ble to deal efficiently with global illumination in general scenes made up of several million geometric primitives. † {fradin,daniel}@sic.univ-poitiers.fr and sebhorna@free.fr Their method distributes the photons into brick maps, en- abling efficient caching and memory coherence. Figure 1: (left) 80 unfurnished floors of our Tower_100 building made up of 1.07 billion triangles; (right) Inside view with global illumination and furniture. In this paper, our goal is to provide a method for out-of- core photon mapping with very large buildings, which are composed of several million polygons with thousands light sources and rooms. Our most complex scene contains one billion unique, non instantiated triangles. We do not make any assumption about the number of polygons contained in each room. We take advantage of a cells and portals data structure for computing view-independent global illumina- tion. Cells and portals are essentially used for favoring data locality. c  The Eurographics Association 2005.