We wish to extract the topology from scanned maps. In previous work [GNY96] this was done by extracting a skeleton from the Voronoi diagram, but this required vertex labelling and was only useable for polygon maps. We wished to take the crust algorithm of Amenta, Bern and Eppstein [ABE98] and modify it to extract the skeleton from unlabelled vertices. We find that by reducing the algorithm to a local test on the original Voronoi diagram we may extract both a crust and a skeleton simultaneously, using a variant of the Quad-Edge structure of [GS85]. We show that this crust has the properties of the original, and that the resulting skeleton has many practical uses. We illustrate the usefulness of the combined diagram with various applications.

Abstract In mapping organizations, the implementation of more automation coupled with the availability of heterogeneous data requires the investigation, adaptation and evaluation of new approaches and techniques. The demand for rapid mapping operations such as database generation and updating is continuously increasing. Due to the rising use of raster data, image analysis techniques have been investigated and tested in this study to introduce automation in the assessment of scanned topographic monochrome maps and Landsat 7 ETM+ imagery for feature separation and extraction in northern Canada. The work focuses on the detection and extraction of lakes -predominant features in the North -as well as on to their spatiotemporal comparison. Various approaches using digital image processing techniques were implemented and evaluated. Thresholding and texture measures were used to evaluate the potential of rapid extraction of certain topographic elements from scanned monochrome maps of northern Canada. A raster to vector approach (R ! V) followed for the vectorization of these extracted features. The extraction of features from Landsat 7 ETM+ imagery involved image and theme enhancement by applying various image fusion and spectral transformations (e.g., Brovey, PCI-IMGFUSE, intensity -hue -saturation (IHS), principal component analysis (PCA), Tasseled Cap, Normalized Difference Vegetation Index (NDVI)), followed by image classification and thresholding. Tests showed that the approaches were more or less feature-dependent, while, at the same time, they can augment and significantly enhance the conventional topographic mapping methods. Following the analysis of the map and image data, change detection between two lake datasets was performed both interactively and in an automated mode based on the non-intersection of old and new features. The various approaches and methodology developed and implemented within a GIS environment along with examples, results and limitations are presented and discussed. Crown

Generating terrain models from contour input is still an important process. Most methods have been unsatisfactory, as they either do not preserve the form of minor ridges and valleys, or else they are poor at modelling slopes. A method is described here, based on curve extraction and generalization techniques, that is guaranteed to preserve the topological relationships between curve segments. The skeleton, or Medial Axis Transform, can be extracted from the Voronoi diagram of a well-sampled contour map and used to extract additional points that eliminate cases of "flat triangles" in a triangulation. Elevation estimates may be made at these points. Based on this approach it is possible to make reasonable estimates of slopes for terrain models, and to extract meaningful intermediate points for triangulated irregular networks (TINs).

Much work has been done in the last few years on various aspects of automated map generalization. However, many of these efforts have been directed to the generalization of individual objects - houses, roads, etc. - while ignoring the spatial relationships between the objects themselves. This problem is particularly apparent where map generalization includes the simplification of contour lines (which may overlap as a result, if no spatial relationships are preserved), or the question of preserving the relationships between different linear features (roads, rivers, railways) that must be cartographically displayed (even if displaced) in the smaller-scale maps after generalization. We here

The concept of a “Marine GIS ” is in some ways an oxymoron: a GIS (Geographical Information System) almost presupposes that “Geography ” equals “Land”. The classical GIS structure is based on manual cartography, with registered transparent overlays of different themes, and the manual extraction of

Abstract: This paper introduces a practical approach to constructing a hybrid 3D metrical–topological model of a university campus or other extended urban region from labeled 2D floor plan geometry. An exhaustive classification of adjacency types is provided for a typical

It is well known that extraction of the skeleton of a polygon from its outline may aid in the perception or classification of its form. It has also been suggested that the `exoskeleton' may be used to express the relationships between objects in space. A new algorithm has been developed that extracts both the boundary and the skeleton of the spatial representation of an object in one easy step, based on local properties of the Delaunay/Voronoi diagram, without requiring additional information, such as point order or polygon labelling. This displays and preserves the fundamental relationships between the boundary and the skeleton that helps considerably in many cartographic problems. Illustrations include contour map input and terrain visualization; watershed and flow estimation from river network input, and drainage network estimation from basin boundaries; topological reconstruction from scanned map input, and text recognition and placement in cadastral maps. The concept of preservation of the `form' of the skeleton suggests methods for map generalization without significant loss of meaning. Spatial uncertainty may also be addressed in terms of the boundary sampling requirements and permissible locational error without loss of the ability to interpret the basic form, spatial relationships and meaning of the map.

document in whole or in part in any medium now known or hereafter created.

GIS as we know it is traditionally a two-dimensional static representation of space, closely related to the paper maps that were its inspiration. While various attempts have been made to define a “3D GIS or a “Dynamic GIS”, in recent years other disciplines have moved much faster in this direction – notably some parts of computer science, computer graphics and game development. This paper looks at this situation, and suggests some remedial actions in the geography (and surveying) communities. These consist primarily of a stronger emphasis on teaching computer algorithms as applied to spatial analysis, as well as a familiarity with the basics of computer graphics and spatial data structures. I hope to show that a modest subset of these tools is sufficient to lead towards the modelling of the third dimension and time. However, one worry remains – is this still GIS?

document in whole or in part in any medium now known or hereafter created. Signature of Author: