Abstract
Road networks are important for modelling the urban geographic environment. It is necessary to determine the spatial relationships of road intersections when using maps to help researchers conduct virtual urban geographic experiments (because a road intersection might occur as a connected cross or as an unconnected bridge overpass). Based on the concept of using different map layers to organize the render order of each road segment, three methods (manual, semi-automatic and mask-based automatic) are available to help map designers arrange the rendering order. However, significant efforts are still needed, and rendering efficiency remains problematic with these methods. This paper considers the Discrete, Crossing, Overpass, Underpass, Conjunction, Up-overlap and Down-overlap spatial relationships of road intersections. An automatic method is proposed to represent these spatial relationships when drawing road networks on a map. The data-layer organization method (reflecting road grade and elevation-level information) and the symbol-layer decomposition method (reflecting road covering order in the vertical direction) are designed to determine the rendering order of each road element when rendering a map. In addition, an “auxiliary-drawing-action” (for drawing road segments belonging to different grades and elevations) is proposed to adjust the rendering sequences automatically. Two experiments are conducted to demonstrate the feasibility and efficiency of the method, and the results demonstrate that it can effectively handle spatial relationships of road networks in map representations. Using the proposed method, the difficulty of rendering complex road networks can be reduced.
Highlights
Road networks are widely distributed in urban environments and have played key roles in a range of urban modelling studies, such as urban growth simulation [1,2], urban transportation modelling [3,4], and city road noise simulation [5,6] studies
The Draw function is provided for external applications; to draw linear map symbols, users can employ customized rendering technologies, such as the Graphic Device Interface plus (GDI+) or Anti-Grain Geometry (AGG) libraries
The spatial relationships of road intersections in a road network can be represented by rendering each drawing-action
Summary
Road networks are widely distributed in urban environments and have played key roles in a range of urban modelling studies, such as urban growth simulation [1,2], urban transportation modelling [3,4], and city road noise simulation [5,6] studies. Based on the principle of drawing higher-grade and higher elevation-level roads later in the rendering process, the proposed method organizes different roads into data-layers and decomposes road symbols into multiple symbol-layers. It generates a range of drawing-actions by combining the data-layers with the different symbol-layers. The proposed method, based on the conclusions related to the spatial relationships of road intersections and includes data organization and symbol decomposition, is discussed in detail, and the “auxiliary-drawing-action-based” method is explained. IBDyadtarLaawyeinrCgotlhleecsteiosno(rhteigdhIeDr aetlaeLvaaytieorCnollelvecetli)ownsi,llebaechloscuactceedsosinvetoIpDoaftatLhaeyperrCevoiloleuctsioIDn a(htaiLgahyeerrCeloelvleacttiioonn (lleovwele)rweillelvbaetilooncaletevdelo).n top of the previous IDataLayerCollection (lower elevation level)
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