The generation of realistic 3D landscape visualisations is already feasible, if data from airborne laser scanning, which allows for a dense and accurate acquisition of the terrain surface, is combined with additional textures from aerial images. While this is true for open areas, the presentation of more complex areas like urban landscapes requires additional processing of this original data. As an example, during the visualisation of buildings from close virtual viewpoints, even small geometric errors which can result from a non-planar triangulation of a building façade may heavily disturb the degree of realism. Another problem is street surfaces, where the laser-based point measurement is disturbed by objects like vehicles, traffic signs or trees. These erroneous points have to be eliminated by suitable filter algorithms, otherwise they will result in disturbing height discontinuities in the street surface to be visualised. Within the approach presented in the paper, the required filter process is supported by the integration of existing street networks. By these means a smoothed 3D shape of the longitudinal axis of the streets can be estimated and expanded to the complete street region. In addition to demonstrating the DEM filter process in street regions, the paper discusses its application to continuous level of detail approaches which are commonly used in the real-time visualisation of such terrain models.