R. Suba

Continuous Road Network Generalization throughout All Scales

Until now, road network generalization has mainly been applied to the task of generalizing from one fixed source scale to another fixed target scale. These actions result in large differences in content and representation, e.g., a sudden change of the representation of road segments from areas to lines, which may confuse users. Therefore, we aim at the continuous generalization of a road network for the whole range, from the large scale, where roads are represented as areas, to mid- and small scales, where roads are represented progressively more frequently as lines. As a consequence of this process, there is an intermediate scale range where at the same time some roads will be represented as areas, while others will be represented as lines. We propose a new data model together with a specific data structure where for all map objects, a range of valid map scales is stored. This model is based on the integrated and explicit representation of: (1) a planar area partition; and (2) a linear road network. This enables the generalization process to include the knowledge and understanding of a linear network. This paper further discusses the actual generalization options and algorithms for populating this data structure with high quality vario-scale cartographic content.

Data Structures for Continuous Generalisation: tGAP and SSC

Spatial zoom and thematic navigation are indispensable functionalities for digital web and mobile maps. Therefore, recent map generalisation research has introduced the first truly smooth vario-scale structure (after several near vario-scale representations), which supports continuous or smooth zooming. In the implementation, the vario-scale representation of 2D geo-information can be stored as a single 3D (2D+scale) data structure. A single uniform scale map in 2D is then derived by computing a horizontal slice through the structure.

An Area Merge Operation for Smooth Zooming

When zooming a digital map it is often necessary that two or more area features must be merged. If this is done abruptly, it leads to big changes in geometry, perceived by the user as a “jump” on the screen. To obtain a gradual merge of two input objects to one output object this chapter presents three algorithms to construct a corresponding 3D geometry that may be used for the user’s smooth zooming operations. This is based on the assumption that every feature in the map is represented in 3D, where the 2D coordinates are the original representation, and 1D represents the scale as a Z value. Smooth zooming in or out is thus equivalent to the vertical movement of a horizontal slice plane (downwards or upwards).