The Degree of Realism of GIS-Based Virtual Landscapes: Implications for Spatial Planning

Communicating planning results within expert groups or to local citizens is crucial for the planning process to be efficient. Although 2-dimensional representations are still predominantly used in spatial planning, recently digital 3Dvisualizations have become more common. However, the validation of simulations of virtual landscapes regarding their degree of realism has so far been neglected in research. By modelling a GIS-based virtual landscape encompassing the region of Schwyz and Ingenbohl-Brunnen in Central Switzerland, it is investigated to which degree the real visually perceived landscape can be validly represented by a digital virtual landscape. 1. GIS-BASED 3D-VISUALIZATION There exist a number of conventional analog as well as digital representation techniques which can be used in spatial planning (see Lange 1999a). The basic elements of the landscape which need to be represented for planning purposes are terrain, built objects and vegetation. Nowadays digital terrain data is widely available at various resolutions. The actual land use information can be represented through imagery acquired through remote sensing. Like terrain data image data is a common data source being used. However, the resolution of satellite imagery is still often fairly low or the recorded color bands are not covering a spectrum as it is perceived by the human eye. For the digital visual simulation a virtual model of the study area consisting of various elements like e.g. a digital terrain model, digital imagery and various kinds of land use data is assembled. The terrain is visualized through the DHM 25 terrain model of the Federal Office for Topography. It is an elevation model based on a 25 m grid derived from the 1 : 25 000 topographic map. In order to get a landscape with texture information, digital imagery can be draped over the terrain. The satellite image used is a Landsat TM scene at 25 m resolution, resampled from 30 m. The digital orthophoto (SwissPhoto) has a resolution of 2.5 m. Although imagery is available which has a higher resolution, for reasons of practicality the lower resolution of 2.5 m is used. Vegetation is represented based on the analysis of the digital topographic map (the so-called 'Pixelmap', scale 1 : 25 000) of the Federal Office for Topography using pattern recognition techniques (Nebiker & Carosio 1995, Stengele 1995). The pattern recognition technique was developed and carried out by the Institute for Geodesy and Photogrammetry at ETHZ. Based on the same principles the Federal Office for Topography is currently producing vector data covering the whole of Switzerland, thereby providing the necessary base data for the general public in the near future. The resulting 2-D data sets are handled through ARC/INFO. The described vegetation can be transformed into the 3-D environment by setting them on the terrain surface and creating polygonal objects on which the appropriate tree textures can be mapped (Hoinkes & Lange 1995). This procedure is done by using Polytrim software which is developed at the Centre for Landscape Research at the University of Toronto (see Danahy & Hoinkes 1995). Also, the footprints of the buildings can be exported from the GIS to the visualization system to create building volumes based on predefined attributes (height of the building). For the detailed representation of built-form texture-mapping is used in the foreground. For this step manual modelling is needed. 'Photogrammetric Week '99' D. Fritsch & R. Spiller, Eds., Wichmann Verlag, Heidelberg, 1999.