Tests whether a Geometry is simple as defined by the OGC SFS specification.
Simplicity is defined for each geom::Geometry type as follows:
- geom::Point geometries are simple.
- geom::MultiPoint geometries are simple if every point is unique
- geom::LineString geometries are simple if they do not self-intersect at interior points (i.e. points other than the endpoints).
- geom::MultiLineString geometries are simple if their elements are simple and they intersect only at points which are boundary points of both elements. (The notion of boundary points can be user-specified - see below).
- Polygonal geometries have no definition of simplicity. The isSimple code checks if all polygon rings are simple. (Note: this means that isSimple cannot be used to test for ALL self-intersections in Polygons. In order to check if a Polygonal geometry has self-intersections, use geom::Geometry::isValid()).
- geom::GeometryCollection geometries are simple if all their elements are simple.
- Empty geometries are simple
For linear geometries the evaluation of simplicity can be customized by supplying a BoundaryNodeRule to define how boundary points are determined. The default is the SFS-standard.
Note that under the Mod-2 rule, closed LineStrings (rings) have no boundary. This means that an intersection at their endpoints makes the geometry non-simple. If it is required to test whether a set of LineStrings touch only at their endpoints, use BoundaryNodeRule::getBoundaryEndPoint(). For example, this can be used to validate that a collection of lines form a topologically valid linear network.
By default this class finds a single non-simple location. To find all non-simple locations, set setFindAllLocations(bool) before calling isSimple(), and retrieve the locations via getNonSimpleLocations(). This can be used to find all intersection points in a linear network.
- See also
- BoundaryNodeRule
