Computational Aesthetics in Graphics, Visualization, and Imaging (2008) P. Brown, D. W. Cunningham, V. Interrante, and J. McCormack (Editors) Expressive Trajectories Luiz Velho †1 , Julio Martins 1 , Alice Bodanzky 2 , Ilana Paterman 1 , and Analivia Cordeiro 1 IMPA – Instituto de Matematica Pura e Aplicada 2 ESDI – Escola Superior de Desenho Industrial Abstract This paper presents Expressive Trajectories, a project for Interactive Digital Art and Contemporary Dance. The project has two main components: X-Motion, a real-time interactive system for live performances; and Chore- ographisms, an interface abstraction for graphical interpretation of motion-paths. This framework is demonstrated through an experiment that includes a choreography of the artist–collaborator for the piece Unsquare Dance. Categories and Subject Descriptors (according to ACM CCS): I.3.8 [Computer Graphics]: Applications 1. Introduction In recent years, the use of multimedia resources, such as live projection and dynamic lighting, has been increasingly ex- ploited in music shows, dance presentations and art perfor- mances [Bul06, Mae04, DWC ∗ 01, Min84]. However, up to now, these powerful visual sources have been applied mostly as an additional element to the set background, thus trans- forming it into a visually dynamic stage [Sch93, SMC94]. The above context motivated us to develop a multidisci- plinary project that aims to combine techniques from Com- puter Graphics, Vision and Animation with applications in Contemporary Dance, Stage Design and Art.Our goal in this project is to push forward the state-of-the-art by calling into the scene real-time interaction and vision techniques. In this way, by integrating motion capture with procedural graph- ics and live displays, we expand the creative possibilities enabling graphical elements to be used, not just as a mere passive set element, but primarily as an active one – a virtual agent capable of interacting with other actors in the scene under the guidance of the director-choreographer. For that goal, we created the X–Motion system which en- ables the design of a virtual dynamic stage that is linked to the dance. The system uses movements of dancers as an in- put for the generation of graphisms that are projected on the set in real-time. Through the system, the choreographer di- rects not only the dancers’ movements, but also graphical † lvelho@impa.br elements that are projected onto the set, which becomes dy- namic and interactive. Thus, these graphisms act as virtual dancers, establishing a partnership and dialogue with real dancers mediated by the choreographer. They can be mod- ified by actions of the dancers, instigating changes to the dancers’ movements as well. The system captures the motion of markers on the dancers’ body to generate trajectories that are represented as curves parametrized in time. Authoring is based on graphi- cal interpretation of movement, thus establishing an associa- tion of motion-paths with visual forms. These motion-paths are coupled with procedural methods which transform them into (re)active shapes. Expressive visual elements are pro- grammed by the director-choreographer using an abstraction that we call choreographisms. This interface defines the syn- tactic and semantic graphical rules to be applied to motion paths during a live performance. An experiment to evaluate the project was conducted with a renowned dancer/choreographer . She is a pioneer on dance-technology and also a specialist on the Laban method. She made use of the system to develop an artistic work called Unsquare Dance. The rest of the paper is structured as follows. In Section 2 we describe the X-Motion system and its architecture. In Section 3 we discuss the concepts used for graphics inter- pretation in the interface Choreographism. In Section 4 we show some results of the performance “Unsquare Dance”. Finally, in Section 5 we conclude with remarks and hints of future directions. c  The Eurographics Association 2008.