Towards a 3D geo-data model to support pedestrian routing in multimodal public transport travel advices
Web based multimodal travel planners are able to generate adequate travel advises for the public transport using timetable information. These travel advises are nowadays lacking detailed pedestrian route advises for the walking parts of a journey. This research focuses on developing a 3D geo data model to support pedestrian route finding for access, change and egress public transport in multimodal travel advises. The research studies the suitability of Oracle spatial 11g to find walk routes in such geo data models. It focus on geo data models to support finding an optimal route for the individual public transport traveller taking into account his specific preferences and constrains (e.g. wheelchair) for the pedestrian part of the journey in a travel advise. Travel time and time pressure, physical effort safety and conform personnel characteristics and vicinity are seen as important aspects of an optimal route. A literature study is done on existing standards and models to investigate approaches to develop such a 3D geo data model.
Based on this literature study a new conceptual geo data model is developed to support pedestrian routing in multimodal travel advises. It uses, similar as in a navigable space model (Slingsby, Raper 2008) a model representing 3D spaces only by their lower surfaces. A Stop Place Model (IFOPT 2007) is taken for it semantics describing and indentifying these spaces relevant for pedestrian routing related to public transport. To persist the geometrical aspects of these lower surfaces in a spatial database the geo data model uses simple feature (OGC 1999) surfaces. The model supports modelling of multiple layered floors and traffic areas which can be seen by a traveller on which “walking around” is possible. It also supports virtual surfaces “hidden paths” with are predefined logic connecting route areas on these floors and traffic areas. As in existing models (Lee 2004) (Stevens, Choi 2006) adjacency and connectivity of spaces are modelled with networks. The developed pedestrian model is new because attributes and behaviour of networks and surfaces are integrated. Important in this geo data model is that no difference is made between in modelling indoor and outdoor spaces. The lower surfaces representing spaces are modelled as objects inherit attributes and behaviour from nodes in a network and therefore called NodeSurfaces. Every NodeSurface is seen as possible connection for a route choice for an optimal pedestrian route. These possible pedestrian connections are modelled by combining connecting NodeSurfaces and using simple feature multiSurface to model it geometrical aspects. In this geo data model these multi surfaces are describing the potential pedestrian connections with attributes and behaviour from links in networks. Important characteristics of this multiSurface (“LinkSurfaces”) are the direction (including up/down in 3D), the accessibility and pedestrian duration for a specific traveller.
A prototype implementing this new geo data model in Oracle 11g was developed. To illustrate and evaluate the new model surfaces relevant in a simple bus stop and a multimodal transport interchange where drawn in Google SketchUp and exported to KML files. These 3D surfaces where used as dataset for optimal route finding in the prototype. This research evaluates this prototype to evaluate the feasibility and suitability of the new geo data model. This prototype was also used to evaluate in suitability of Oracle spatial 11g to find walk routes in such pedestrian models. The results of the conceptual model are promising especially when modelling hidden paths. It was possible to implement the geo data model in Oracle 11g. Oracle 11g network shortest route capabilities for logical network turned out to be suitable for finding the optimal route for individual travellers with specific speed and accessibility properties. Due to the limitation that Oracle 11G does not support 3D distance calculation in geographic 3D all distances in pedestrian speed calculation were done on the geodetic surface. Optimal pedestrian routes where exported to KML files and visualisation was done with Google earth. Limitations were found for visualisation of surfaces below ground level (underpasses). The concepts of LinkSurfaces used to represent 3D pedestrian spaces in the proposed geo data models worked well in the prototype. This concept combing characteristics from links in a network and characteristic from OGC simple feature multi surfaces, is a simple, effective and well structured way to represent complex 3D spaces used by pedestrian routes in a geo data model.