Rendering IEEE Computer Graphics and Applications he realistic modeling of vegetation is an important problem in computer graphics. Vegetation adds a significant dimension of realism to a scene. Trees, in particular, form an integral part of architectural landscapes. Many techniques 1, 2-4 and modeling packages (for example, Tree Professional Software and MaxTrees) have been developed for constructing a tree of a particular type. However, variations between two trees of a single type can be very significant, depending heavily on factors ranging from growth conditions (such as the amount and direction of sunlight reaching the tree) to human intervention (such as pruning branches). Sometimes you want to create a 3D tree model resembling a specific tree. Such a need might arise, for example, in planning modifications to an existing architectural scene; modeling proposed changes requires a faithful model of the existing scene. The techniques and packages currently available don't provide sufficient control over the final shape and appearance of the model to be useful for reconstructing specific trees. Thus, we propose a solution for reconstructing a faithful 3D model of a foliaged tree from a set of instrumented photographs. Procedural techniques have been widely used to generate detailed 3D models. 5 Their power lies in having a high database amplification factor, or their ability to generate a wide range of complex structures from a small set of specified parameters. However, because of the nature of their power, the procedural models are hard to control, since a small perturbation in the parameter space results in a significant change in the resulting structure. Perhaps this is the reason that little work has been done on inverse procedural models-namely, forcing a procedural model to reproduce an entity that already exists. Because it's difficult to control procedural models, an approach to construct an inverse procedural model by a parameter space search appears intractable; hence, other techniques need to be developed. In a recent work, 6 Sakaguchi recognizes the power of the procedural growth models, but points out that the difficulties of accurately inferring parameters of such a model has driven him to develop another, unrelated approach. Sakaguchi seeds small branches around the tree's 3D shape, then gradually merges them together into larger branches. Because this procedure yields a number of undesirable artifacts, he corrects them using a number of heuristics. While this approach has produced some reasonable results, it can't be connected easily to the highly developed field of procedural modeling of vegetation. By contrast, our approach aims to extract enough information from a set of images to let a procedural model be used. In this article, we propose a hybrid approach to solving the inverse problem of reconstructing a foliaged tree. Our method involves first constructing the skeleton (trunk and the major branches) of the tree, and then applying an L-system starting from this skeleton. L-systems are one of the better-known procedural models in the graphics community, especially after their popularization by Lindenmayer and Prusinkiewicz. 7 The "Related Work" sidebar provides some background on L-systems. Structurally, trees are immensely complex. With that in mind, we can only hope for a reconstruction scheme that produces a similar tree which, although it differs significantly from the original in structure, nevertheless retains its overall impression. This is the reason we've restricted the scope of this project to foliaged trees: it's hard to reproduce the impression of an unfoliaged (winter) tree without achieving a high-fidelity structural reconstruction of its branching system. With foliaged trees, however, a plausible branching structure suffices to preserve the overall impression of the original, since we can't see the original branches. Observing a foliaged tree, we infer an intuitive branching structure from the shape of the foliaged tree and our knowledge of trees in general. This process serves as the motivation for our approach. Despite the excellent results on synthetic L-systems' topiary in Prusinkiewicz et al., 8 in which bushes are grown and pruned to fill predefined shapes bushes are only remotely related to trees. The impressions produced by a
Shlyakhter et al. REF build 3D model of foliaged trees from instrumented (rather than uncalibrated) photographs with the goal of generating realistic trees in computer graphics applications.
Reconstructing 3D Tree Models from Instrumented Photographs
IEEE Computer Graphics and Applications
Computer Science