Namespace NetTopologySuite.Operation.Valid

Classes for testing the validity and simplicity of geometries, as defined in the OGC Simple Features specification.

Classes

ConnectedInteriorTester

This class tests that the interior of an area Geometry (Polygon or MultiPolygon) is connected. An area Geometry is invalid if the interior is disconnected. This can happen if:

• a shell self-intersects,
• one or more holes form a connected chain touching a shell at two different points,
• one or more holes form a ring around a subset of the interior. If a disconnected situation is found the location of the problem is recorded.

ConsistentAreaTester

Checks that a GeometryGraph representing an area (a Polygon or MultiPolygon ) is consistent with the SFS semantics for area geometries. Checks include: Testing for rings which self-intersect (both properly and at nodes). Testing for duplicate rings. If an inconsistency if found the location of the problem is recorded.

IndexedNestedRingTester

Tests whether any of a set of LinearRings are nested inside another ring in the set, using a spatial index to speed up the comparisons.

IsSimpleOp

Tests whether a Geometry is simple as defined by the OGC SFS specification.

Simplicity is defined for each Geometry type as follows:

• Pointgeometries are simple.
• MultiPointgeometries are simple if every point is unique
• LineStringgeometries are simple if they do not self-intersect at interior points (i.e.points other than the endpoints). Closed linestrings which intersect only at their endpoints are simple (i.e. valid LinearRingss.
• MultiLineStringgeometries 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).
• Polygonalgeometries have no definition of simplicity. The IsSimple code checks if all polygon rings are simple. (Note: this means thatIsSimple cannot be used to test for all self-intersections in Polygon s. In order to check if a IPolygonal geometry has self-intersections, use IsValid.
• GeometryCollectiongeometries are simple if all their elements are simple.
• Empty geometries are simple

For ILineal geometries the evaluation of simplicity can be customized by supplying a IBoundaryNodeRule to define how boundary points are determined. The default is the SFS-standard Mod2BoundaryRule.

Note that under the Mod-2 rule, closed LineStrings (rings) have no boundary. This means that an intersection at the endpoints of two closed LineStrings makes the geometry non-simple. 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 EndpointBoundaryRule. 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 FindAllLocations before calling IsSimple(), and retrieve the locations via NonSimpleLocations. This can be used to find all intersection points in a linear network.

IsValidOp

Implements the algorithms required to compute the IsValid method for Geometrys. See the documentation for the various geometry types for a specification of validity.

RepeatedPointTester

Implements the appropriate checks for repeated points (consecutive identical coordinates) as defined in the NTS spec.

TopologyValidationError

Contains information about the nature and location of a Geometry validation error.

Enums

TopologyValidationErrors

Contains information about the nature and location of a Geometry validation error.