A Topology is the spatial relationship between connecting or adjacent features in a geographic data layer (for example, arcs, nodes, polygons, and points). Topological relationships are used for spatial modeling operations that do not require coordinate information. Topology defines and enforces data integrity rules (for example, there should be no gaps between polygons). It supports topological relationship queries and navigation (for example, navigating feature adjacency or connectivity), supports sophisticated editing tools, and allows feature construction from unstructured geometry (for example, constructing polygons from lines).
A geometric network is an object commonly used in geographic information systems to model a series of interconnected features. Data about systems such a Water distribution system or an Electrical distribution system usually participate in a Geometric Network. Topology about the individual features needs to be analysed before a geometric network can be built.
FME offers a number of transformers to help build topology and analyse geometric networks.
Example 1: Build Topology and Calculate Route Length
The TopologyBuilder transformer is used in this example to calculate lengths along a line between node points. e.g. lengths between bus stops on a bus route.
Example 2: Calculate Emergency Response Travel Times
This example illustrates how to calculate emergency response travel time contours (isochrones) from street and parcel data. The NetworkCostCalculator is the central transformer in this example.
Example 3: Calculate Strahler Stream Order Numbers
This example demonstrates how to use the StreamOrderCalculator transformer to assign Strahler or Horton order numbers to streams in a river network.
Example 4: Remove Intersections from Line Segments
This example demonstrates, by making use of the TopologyBuilder and NetworkTopologyCalculator, how it possible to join line segments together based on the angle between them.
Example 5: Finding the Shortest Path Between a Start and End Point
This example demonstrates how to use the ShortestPathFinder to calculate the shortest path from a source node to a destination node on a given network. A path can be weighted by its length or by an attribute.
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