Visualisation of Scale Dependencies in Surface Models

TitleVisualisation of Scale Dependencies in Surface Models
Publication TypeConference Paper
Year of Publication1999
AuthorsWood, J
Conference NameICA 1999
Conference LocationOttawa, Canada

This paper examines some of the techniques available for the visualisation of surface models of terrain. In particular it concentrates on those visualisation processes that involve examining and understanding scale dependency within a landscape. Scale dependency is defined in this context as the characteristics of a point on a terrain model that vary when measured over different spatial extents. Scale dependency is an important property of a surface as it allows us to identify critical points on a landscape and critical scales of analysis. Identifying scale dependency is an important part of surface generalisation, which in turn is necessary for efficient surface visualisation. Two methods of surface visualisation are implemented using the Java programming language and the OpenGL graphics library. The first involves creating a '3-dimensional' perspective rendering of the terrain model which can be explored by 'flying' over the surface in real time. This process exploits our cognitive ability to assimilate visual information at a variety of scales simultaneously. Near, foreground, large scale detail can be represented at the same time as far, background, small scale generalisation. By 'flying' over a landscape, the regions of the terrain represented at large and small scales can be changed continuously. By allowing an observer to change viewpoint interactively, the spatial organisation of scale dependency can be explored. The second method of visualisation involves calculating morphometric measurements over a range of grid resolutions. Users of the system can interactively interrogate parts of the landscape and are presented with graphical summaries of how these measurements vary with grid resolution. Measurements vary from simple surface properties such as slope and curvature, to higher order structural partitions of the landscape such as drainage basins and ridge networks. The approach described here is new in that it makes the visualisation process central to terrain analysis, and considers analysis at scales other than that imposed by the grid resolution of the underlying elevation model. The approach is accessible since it implements the visualisation on low-cost PC platforms using freely available software.