GEOS  3.9.0dev
geos::operation::overlay Namespace Reference

Contains classes that perform a topological overlay to compute boolean spatial functions. More...

## Classes

class  EdgeSetNoder
Nodes a set of edges. More...

class  LineBuilder
Forms JTS LineStrings out of a the graph of geomgraph::DirectedEdge created by an OverlayOp. More...

class  MaximalEdgeRing
A ring of DirectedEdges which may contain nodes of degree > 2. More...

class  MinimalEdgeRing
A ring of Edges with the property that no node has degree greater than 2. More...

class  OverlayNodeFactory
Creates nodes for use in the geomgraph::PlanarGraph constructed during overlay operations. NOTE: also used by operation::valid. More...

struct  overlayOp
OverlayOp::overlayOp Adapter for use with geom::BinaryOp. More...

class  OverlayOp
Computes the geometric overlay of two Geometry. More...

class  PointBuilder
Constructs geom::Point s from the nodes of an overlay graph. More...

class  PolygonBuilder
Forms Polygon out of a graph of geomgraph::DirectedEdge. More...

## Detailed Description

Contains classes that perform a topological overlay to compute boolean spatial functions.

The Overlay Algorithm is used in spatial analysis methods for computing set-theoretic operations (boolean combinations) of input Geometrys. The algorithm for computing the overlay uses the intersection operations supported by topology graphs. To compute an overlay it is necessary to explicitly compute the resultant graph formed by the computed intersections.

The algorithm to compute a set-theoretic spatial analysis method has the following steps:

• Build topology graphs of the two input geometries. For each geometry all self-intersection nodes are computed and added to the graph.
• Compute nodes for all intersections between edges and nodes of the graphs.
• Compute the labeling for the computed nodes by merging the labels from the input graphs.
• Compute new edges between the compute intersection nodes. Label the edges appropriately.
• Build the resultant graph from the new nodes and edges.
• Compute the labeling for isolated components of the graph. Add the isolated components to the resultant graph.
• Compute the result of the boolean combination by selecting the node and edges with the appropriate labels. Polygonize areas and sew linear geometries together.