Robert G. Laycock

Automatically generating large urban environments based on the footprint data of buildings

This paper focuses on the generation of three dimensional models of large urban/suburban environments. Previous work on the reconstruction of particular environments is based on multiple overlapping aerial or street level images. Unfortunately these approaches do not extend well to large environments. The main reasons for this are that they require expensive high-resolution aerial images and a labour intensive modelling or data capture procedure. Consequently methods have been developed to generate large urban environments based on environmental data such as elevation data or building footprints. This permits the model to be based on actual data for the area being modelled and at a cost far less than that of aerial images. By reducing the data given to the model generation procedure various parameters are undetermined. These include roof style and textured appearance. This paper focuses on the use of building footprint information to construct a three dimensional model. It uses LIDAR data to give the buildings a height value and assigns them a roof using new techniques for roof modelling.

Exploring cultural heritage sites through space and time

Traveling through a single virtual environment only tells part of the story; a particularly interesting aspect is to illustrate how an area has developed over time. This article presents a unified approach to illustrating four-dimensional data concerning a cultural heritage site. The proposed framework provides a semi-automatic approach to both reconstructing the environment and bringing all the time-dependent models into an intuitive visualization package. For each time period considered for reconstruction, the system requires a set of building footprint maps depicting the layout of the environment plus a few statistics. The statistics govern the construction of three-dimensional building models, allowing each buildings architectural style, typical building height, and roof style to be altered. This information is automatically processed and converted into a form that can be visualized. By integrating high quality landmark buildings from laser scanning or interactive modelling packages into the automatically generated scene, the cultural heritage site is realized both in a spatial and temporal context. The visualization is achieved via a 4D navigable movie which is presented using two concrete implementations written using Flash and OpenGL. The OpenGL-based implementation allows a collection of 3DS Max scenes to be automatically visualized requiring only a set of camera paths identified by the user.

Cultural Heritage: Aligning archive maps and extracting footprints for analysis of historic urban environments

Archive cartography and archaeologists sketches are invaluable resources when analysing a historic town or city. A virtual reconstruction of a city provides the user with the ability to navigate and explore an environment which no longer exists to obtain better insight into its design and purpose. However, the process of reconstructing the city from maps depicting features such as building footprints and roads can be labour intensive. In this paper we present techniques to aid in the semi-automatic extraction of building footprints from digital images of archive maps and sketches. Archive maps often exhibit problems in the form of inaccuracies and inconsistencies in scale which can lead to incorrect reconstructions. By aligning archive maps to accurate modern vector data one may reduce these problems. Furthermore, the efficiency of the footprint extraction methods may be improved by aligning either modern vector data or previously extracted footprints, since common elements can be identified between maps of differing time periods and only the difference between the two needs to be extracted. An evaluation of two alignment approaches is presented: using a linear affine transformation and a set of piecewise linear affine transformations.

GPU techniques for creating visually diverse crowds in real-time

Real-time crowds significantly improve the realism of virtual environments, therefore their use has increased considerably over the last few years in a variety of applications, including real-time games and virtual tourism. However, due to current hardware limitations, crowd variety tends to be sacrificed in order for the crowd simulation to execute in real-time, which decreases the quality and realism of the crowd. Currently the little variety that is incorporated in real-time crowds tends to be applied by modulating each avatar with random colours, which has a detrimental effect on the texture quality. Furthermore, the existing crowd variety is often hard to define and control. To overcome these problems a set of techniques are presented, which defines and controls crowd variety, to further improve on current variety and quality of crowds. These techniques permit variety to be introduced: by changing the body mass via the application of a displacement map onto the mesh; by scaling the skeleton of the avatar; by applying HSV colour shifts to different parts of the avatar; and by transferring textures between avatar models. The appearance of the avatars under animation is also improved via the use of muscle displacement within the mesh. With the new techniques, the visual quality of the crowd is improved due to the increase in diversity.

Technical Section: Automatic generation, texturing and population of a reflective real-time urban environment

In this paper a novel technique is presented for representing a building facades visual appearance in a large virtual urban environment. A fully automatic modelling system is utilised, capable of generating both the terrain and buildings for a 500mx500m urban environment composed of over 120K triangles. Applying the procedural texture generation approach permits the realisation of a large variation in the building facades appearance, whilst remaining within the time constraints of an interactive simulation. The approach is efficient in terms of its memory usage and exploits the recent advances in graphics hardware. By procedurally generating the wall textures, the technique opens the possibility for interaction between various elements of a virtual environment, such as its inhabitants. This is evident in the rendering engine developed, which brings reflections of both the static geometry and the dynamic virtual humans for all window panes into the real-time domain. Height and navigation maps are automatically created, allowing the virtual humans to be automatically populated within the scene. From a dynamic human model cached animations and static billboard impostors are created efficiently on load, allowing for complete model flexibility.

Rapid generation of urban models

This paper discusses existing methods for rapidly generating models of real scenes. In particular it focuses on the use of these methods in reconstructing urban models. The major work in this area has been conducted using images, however, methods have also been developed that use high-resolution digital elevation models. To accomplish the goal of rapidly reconstructing an urban environment many cues in the images are used. These include observing the light reflected from a surface and the disparity between the set of corresponding points in two overlapping images. We will discuss how these cues are used to reconstruct the three-dimensional shape.

Haptic navigation and exploration of high quality pre-rendered environments

Visualising in real-time high quality virtual environments, which are suitable for cultural heritage and virtual tourism, is often a challenging endeavour. This is primarily, due to the cost of rendering complex architectural structures. Incorporating the sense of touch into real time environments enhances a users experience, leading towards a higher level of immersion. However, the confining requirement of the haptic feedback loop to cycle at 1000Hz has led to many applications employing lower quality scenes. In this paper a technique is presented which permits high quality pre-rendered animations of dynamic environments to be both visualised and navigated at high interactive rates. In particular, the approach provides the user with the ability to touch the content of the animations and to freely orientate themselves in any direction, leading to haptically aware movies. Consequently, this permits an exploration of an otherwise prohibitively complex scene consisting of large volumes of geometry and texture maps, combined with realistic lighting models. This component is illustrated within a virtual tour framework enabling users to navigate semi-prescribed routes using haptic feedback both in a spatial and temporal context.

Fuzzy Logic Controlled Pedestrian Groups in Urban Environments

Populating an urban environment realistically with thousands of virtual humans is a challenging endeavour. Previous research into simulating the many facets of human behaviour has focused primarily on the control of an individual’s movements. However, a large proportion of pedestrians in an urban environment walk in groups and this should be reflected in a simulation. This paper, therefore, proposes three fuzzy logic engines in order to adjust the speed of the multi level groups in urban environments. The proposed nested multiple fuzzy logic engines maintain the balance between desired speed, main group and sub group configurations. Thus, a natural and non-rigid group-based locomotion is achieved in urban settings. The realism of the presented techniques is verified by comparing them with statistics acquired from a study on real human behaviour. It is shown that the inter-personal distances between group members, the speed of individuals and the speeds of pedestrians in groups are consistent with their real counterparts.

A Key-Pose Caching System for Rendering an Animated Crowd in Real-Time

We present a method to accelerate the visualization of large crowds of animated characters. Linear‐blend skinning remains the dominant approach for animating a crowd but its efficiency can be improved by utilizing the temporal and intra‐crowd coherencies that are inherent within a populated scene. Our work adopts a caching system that enables a skinned key‐pose to be re‐used by multi‐pass rendering, between multiple agents and across multiple frames. We investigate two different methods; an intermittent caching scheme (whereby each member of a crowd is animated using only its nearest key‐pose) and an interpolative approach that enables key‐pose blending to be supported. For the latter case, we show that finding the optimal set of key‐poses to store is an NP‐hard problem and present a greedy algorithm suitable for real‐time applications. Both variants deliver a worthwhile performance improvement in comparison to using linear‐blend skinning alone.

Distributing Pedestrians in a Virtual Environment

Distributing a collection of virtual humans throughout a large urban environment, where limited semantic information is available, poses a problem when attempting to create a visually realistic real time environment. Randomly positioning agents within an urban environment will not cover the environment with virtual humans in a plausible way. For example, areas of the urban space that are more frequently used should have a higher population density both at the start and during the simulation. It is infeasible to manually identify areas in the urban environment which should be crowded or sparsely populated when considering a scalable method, suitable for large environments. Consequently, this paper combines and extends techniques from spatial analysis and virtual agent behaviour simulations to develop a system capable of automatically distributing pedestrians in an urban environment. In particular, it extends the pointbased space syntax technique to enable the automatic analysis of a large urban environment in the presence of limited contextual information. This analysis specifies a set of population densities for areas in the environment and these values are used to initialise the locations of all the virtual humans in the environment. In addition to the initialisation stage the population densities in each area are consulted to ensure that the correct distribution of virtual humans is maintained throughout the simulation. The system is tested on an arbitrary section of a real city and comparisons of the characteristic parts of the test environment are correlated with the pedestrian movements.