Collision problem: Characteristics for a Taxonomy D. Borro, J. Hernantes Ceit Manuel de Lardizábal 15 20018 San Sebastián, Spain A.García-Alonso EHU Manuel de Lardizábal 1 20018 San Sebastián, Spain L. Matey Tecnun (University of Navarra) Manuel de Lardizábal 13 20018 San Sebastián, Spain {dborro@ceit.es, jhernantes@ceit.es, alex.galonso@ehu.es, lmatey@tecnun.es} Abstract The Collision problem appears within many fields. The specific characteristics that can be identified in different problems lead to the broad set of specialized algorithms that appear in the literature. This paper deals with the first step needed to address the Collision Problem Taxonomy challenge: a survey that compiles and suggests a set of characteristics that could be used to discriminate collision problems, i.e. to generate the taxonomy. 1. Introduction The Collision problem appears within many fields of interest like Geovisualization, Urban Walkthroughs, Robotics or Simulation. Surveys within this topic sometimes compile algorithms, others use applications as the compiling criterion. This survey has a different goal: it is the first step needed to address the Collision Problem Taxonomy challenge: a survey that compiles the characteristics that will be used to discriminate collision problems, i.e. to generate the taxonomy. Although surveys and technical papers make reference to characteristics, there is a lack of systematization. Lin and Gottschalk [1] came near to this objective when they commented some characteristics: queries (see Section 2), pair vs. nbody (Section3), static vs. dynamic (Section 4) and rigid vs. deformable. A taxonomy is required because visualization systems are increasing the scope of problems they must deal with. For instance, geographical visualization is not limited to high altitude flights where the collision problem can nearly be neglected; low flying requires the integration of specific collision algorithms [2]. Even more, geographical visualization data is not restricted to height-maps and terrain textures (see Figures 1 and 2). Now urban models “emerge” from the terrain and each day more demanding links to data bases increase the range of models and information that must be displayed: even physical interaction through haptics. So, visualization systems, in this and in many different areas, must be able to distinguish the characteristics of the data set within the actual navigation range. Also they should identify the characteristics of the current task requested by the user. With this knowledge, applications should apply the most appropriated algorithms. Surveys use different classification criteria [1, 3, 4, 5], for instance, some gather algorithms for non- polygonal models [1], while others consider simple primitives [3]. Although some technical papers are not general surveys, they provide a valuable compilation of previous work [6, 7, 8, 9]. Before entering the goal of the paper, applications will be summarized. Robotics has studied the collision problem in detail [10]. Some problems can be pre-processed, so they are no real time systems, but in most cases the problem must be solved on-line. Physical Simulation covers many engineering analysis like automobile crash simulations [11] or mechanism analysis [12]. Collisions have been often considered by Virtual Reality applications. Some simulate physical environments so that operators can visualize, explore and interact with objects of the virtual environment [13, 14]. Simple VR-CAD applications can make measures and interference analysis among objects [15]. There are applications that deal with virtual prototypes to verify assemblies or carry out maintenance tasks [16]. Collision response is used to control force feedback devices, in order to provide realistic tactile sensations [17, 18, 19]. Animation often addresses collisions, as in cloth [20, 21] and herd-flock problems [22, 23]. Collisions also play a role for achieving realism in games [24]. Each one of the following sections will deal with one characteristic but before going on, one question should be considered: whether the geometric model used to describe the scenario is a characteristic of a given collision problem. In first place, one distinction must be proposed: which geometric model is the native “source” and which one has been derived from the native one as an algorithmic requirement to solve the collision problem. A derived model is more related to the algorithms, i.e. the ways to solve the problem, than to the characteristics that describe the problem. An analysis of