Spatial Databases and GIS Solution for Sheet 4

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Technische Universität Braunschweig Institut für Informationssysteme http://www.ifis.cs.tu-bs.de Karl Neumann, Sarah Tauscher

Spatial Databases and GIS Solution for Sheet 4

Exercise 1 (Label Placement within Polygons)

1. Determine a baseline for label placement within the given polygon using a) the Schoppmeyer/Heisser procedure b) the Petzold/Plümer procedure

2. Give an example of a polygon whose Voronoi skeleton isn’t connected.

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Exercise 2 (Generalization of buildings)

1. Generalize the building given below using the Douglas/Peucker algorithm.

E.g.: g = 1. In the first step there are two most significant points (red) above and be- neath the line between the points with the greatest distance → two possibilities for each polygon half (a) and b)). Only the most significant points, which are further away than g are shown.

1. iteration

a) b)

2. iteration

a) b)

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3. iteration

a) b)

4. iteration

a) b)

For the upper half both ways lead to the same result for the lower half the results are different → two possible solutions for the whole polygon.

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2. Can you think of a strategy for building generalization that guarantees the preserva- tion of right angles?

a) Replace parallel lines (blue) with short distance with one line (green).

b) Define valid forms for buildings, chose the one that fits best.

c) Rasterize the building using a coarse grid.

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Exercise 3 (Basic Generalization Operations)

1. Which basic generalization operation was used in the marked areas?

2. Give examples for all eight basic generalization operations Symbolization

Selection, Simplification

Classification, Simplification

Simplification

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Typification

Enlargement

Symbolisation

Classification

Merge