Section: New Results
2 D1/2 informed spatial subdivision scheme
Participant : Fabrice Lamarche [ contact ] .
Navigation inside virtual environments has a key role in behavioural animation of a virtual human. This process is continuously used for several sorts of interactions (moving to take something, to watch something...). Navigation and path planning are based on a suitable representation of the 3D database in a form enabling path planning and collision avoidance with static obstacles. But a suitable representation of the geometry is not sufficient as a part of the behaviour is related to the semantic of the environment. Most of time, 3D environments are modeled using well known 3D modelling tools such as 3DS Max, Maya and others. Such environments are not informed neither well organized to be directly used in the field of behavioral animation. That is why we propose a model of 2 D1/2 spatial subdivision, enabling navigation and path planning on unflat surfaces while describing the semantic of the different zones.
Instead of conceiving a dedicated tool constraining designers, we propose to label the 3D objects with their name and type in order to inform 3D environments. This information will be used as a key to access a typed database enabling the extraction of semantic information related to the object.
In order to handle navigation and path planning on non flat surfaces (stairs?), we propose a 2 D1/2 spatial subdivision scheme. Starting from the 3 D database (Cf. fig. 26 (a)), two maps are created:
The 2 D1/2 map (Cf. 26 (b)) is an exact decomposition of the environment into convex cells. Borders of those cells correspond to a change of slope, a step, a bottleneck, a change of semantic type or 3 D object name. This map is used to handle low level navigation: determining the height associated to a footprint, computing visibility information. It also links cells to semantic information by keeping identifiers related to the objects of the 3 D database. This way, virtual humans can easily access the semantic information related to the environment they evolve in.
The 2D map (Cf. 26 (c)) is a simplification of the 2 D1/2 map. In this map, borders of convex cells represent a change of semantic type, a step or an identified bottleneck. This map simplifies the previous one by merging cells with similar semantic thus reducing the number of cells used during path planning.
Semantic information is stored inside an object oriented database (we intensively use notions of classes and inheritance). This database contains two types of information: semantic information related to the environment and archetype description. The semantic information associates objects types to their related information. The archetype database contains a hierarchical description of types of agents navigating inside the virtual world (pedestrians, cars?). In order to correlate archetypes to their respective navigation zones, a relational system is provided. It associates archetypes to types of zones in order to specify their navigation behavior (preference, cost?). As types of zones and archetypes are described using inheritance notions, instantiation of relations also use this property in order to provide a system enabling a concise and generic description. For example, if humanoids can navigate on sidewalks and if a crosswalk inherits from sidewalk, a relation between humanoid and sidewalk will automatically take the crosswalk into account during path planning and navigation. Thanks to this information, we are able to generate agent oriented path planning graphs used to create more realistic navigation behaviors. This information is also useful to focus agent attention to relevant zones i.e. zones they navigate in.
Thanks to this model, semantic information can easily be associated to the geometry of the environment. The spatial subdivision process, by keeping this information and organizing geometry, enables a rapid integration of virtual humans inside complex and structured environments containing necessary information to handle realistic navigation. Actually, this system is used to handle navigation, but future works will focus on creating a relation between the environment and the BIIO model (cf paragraph 6.13 ), in order to provide a full framework enabling fast integration of behavioral simulations in informed environments.