Virtual Reality in Brazil 2011 Reproducing virtual characters Roberto C. Cavalcante Vieira n , Creto A. Vidal, Joaquim Bento Cavalcante-Neto Department of Computing, BL. 910, Campus do Pici, Federal University of Ceara ´, Fortaleza 60455-760, CE, Brazil article info Article history: Received 9 June 2011 Received in revised form 1 December 2011 Accepted 5 December 2011 Available online 30 December 2011 Keywords: Modeling of virtual characters Genetic inheritance Reproductive simulation abstract Many virtual reality applications and games need a large number of virtual characters. Some of these applications require, in addition to the quantity, the simulation of kinship and evolution, not only of human character models, but also of different types of animals, toon models or other creatures. Some applications also require interactions between isolated populations with well-defined ethnic char- acteristics. The identification of similar traits between individuals of the same family is crucial to providing increased realism to many of these systems. The main difficulty in these situations is to generate models automatically, in real time, which are physically similar to a given population or family. In this paper, we extended our previous work, in which the reproduction of diploid beings is mimicked to produce character models that inherit genetic characteristics from their ancestors. Unlike morphing techniques, in our method, it is possible that a genetic characteristic from an ancestor be manifested only after a few generations. & 2011 Elsevier Ltd. All rights reserved. 1. Introduction In many applications of virtual reality and computer games, it is necessary to populate the environments with virtual characters. The demand for realistic models that meet the current needs of new technologies and applications has become a major challenge. Additional challenges are posed by applications, such as life- simulation computer games and internet-based virtual worlds, which require simulation of kinship and interaction between isolated populations of different types of creatures with well- defined ethnic characteristics. Sometimes, populating a virtual environment is a process that occurs dynamically during an application run. When populations with distinct ethnic charac- teristics are given contact, due to migration, for example, it is reasonable to expect that, over time, the original populations will intermix and the resulting population of descendants will present mixed traits (genetically determined characteristics) from ances- tors. The problem we address in this paper is the automatic transfer of traits of the whole body of different types of creatures, through simulated diploid reproduction, which is an extension of our previous work [15] for use in virtual reality systems (see Fig. 1). In Section 2, we present some of the most relevant related works. In Section 3, we discuss concepts of anthropometry and some recent studies that relate an individual’s physical appearance to the action of genes. In Section 4, we summarize the important biological concepts of diploid reproduction. In Section 5, the architecture of character reproduction is defined. In Section 6, case studies are provided, which illustrate the general process that is described in Section 5. In Section 7, we present our conclusions. 2. Related work DeCarlo et al. [4] devised a system that is capable of generating facial models for virtual reality applications automatically. Their study, which was one of the first to use anthropometric techniques [10] for face generation, inspired several other studies. DeCarlo used B-Spline surfaces to construct a base model, which respected established anthropometric measurements and perturbed those measurements randomly within predefined ranges, to generate other models. Blanz and Vetter [2] treated faces as members of a vector space. Thus, starting from a database of faces that was captured through the scanning of real subjects, they used Principal Component Analysis (PCA) to determine a set of face basis vectors that could be linearly combined to generate new faces within that vector space. They could generate realistic models with a large amount of variability. Praun et al. [11] used parameterization techniques to combine features of two or more models with different topologies, generating interpolated models. Although their morphing technique showed interesting results, defining the parameters required con- siderable human effort. Kahler et al. [6] built a generic model with anatomical layers (skin, muscles and bones) that were associated with anthropometric landmarks and, based on anthropometric information of individuals at different ages, simulated facial changes in different stages of life. Allen et al. [1] extended Blanz and Vetter’s Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/cag Computers & Graphics 0097-8493/$ - see front matter & 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.cag.2011.12.006 n Corresponding author. Tel.: þ55 85 3366 9847; fax: þ55 85 3366 9837. E-mail addresses: roberto@lia.ufc.br (R.C.C. Vieira), cvidal@lia.ufc.br (C.A. Vidal), joaquimb@lia.ufc.br (J.B. Cavalcante-Neto). Computers & Graphics 36 (2012) 80–91