Class CoverageSimplifier

Simplifies the boundaries of the polygons in a polygonal coverage while preserving the original coverage topology. An area-based simplification algorithm (similar to Visvalingam-Whyatt simplification) is used to provide high-quality results. Also supports simplifying just the inner edges in a coverage, which allows simplifying "patches" without affecting their boundary.

The amount of simplification is determined by a tolerance value, which is a non-negative quantity. It equates roughly to the maximum distance by which a simplified line can change from the original. (In fact, it is the square root of the area tolerance used in the Visvalingam-Whyatt algorithm.)

The simplified result coverage has the following characteristics:

It has the same number of polygonal geometries as the input
If the input is a valid coverage, then so is the result
Node points (inner vertices shared by three or more polygons, or boundary vertices shared by two or more) are not changed
Polygons maintain their line-adjacency (edges are never removed)
Rings are simplified to a minimum of 4 vertices, to better preserve their shape
Rings smaller than the area tolerance are removed where possible. This applies to both holes and "islands" (multipolygon elements which are disjoint or touch another polygon at a single vertex). At least one polygon is retained for each input geometry (the one with largest area).

This class supports simplification using different distance tolerances for inner and outer edges of the coverage(including no simplfication using a tolerance of 0.0). This allows, for example, inner simplification, which simplifies only edges of the coverage which are adjacent to two polygons. This allows partial simplification of a coverage, since a simplified subset of a coverage still matches the remainder of the coverage.

The class allows specifying a separate tolerance for each element of the input coverage.

The input coverage should be valid according to CoverageValidator. Invalid coverages may still be simplified, but the result will likely still be invalid.

NOTE:
Due to different implementations of the PriorityQueue classes used in JTS and NTS the results of the CoverageSimplifier's simplification methods are not guaranteed to be the same. Nonetheless both results are valid.

Inheritance

object

CoverageSimplifier

Inherited Members

object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.ReferenceEquals(object, object)

object.ToString()

Namespace: NetTopologySuite.Coverage

Assembly: NetTopologySuite.dll

Syntax

public sealed class CoverageSimplifier

Remarks

FUTURE WORK

Constructors

| Edit this page View Source

CoverageSimplifier(Geometry[])

Create a new coverage simplifier instance.

Declaration

public CoverageSimplifier(Geometry[] coverage)

Parameters

Type	Name	Description
Geometry[]	coverage	A set of polygonal geometries forming a coverage

Properties

| Edit this page View Source

RemovableRingSizeFactor

Gets or sets a value indicating the factor applied to the area tolerance to determine if small rings should be removed. Larger values cause more rings to be removed. A value of 0 prevents rings from being removed.

Declaration

public double RemovableRingSizeFactor { get; set; }

Property Value

Type	Description
double

| Edit this page View Source

SmoothWeight

Gets or sets a value inidcating the weight influencing how smooth the simplification should be. The weight must be between 0 and 1. Larger values increase the smoothness of the simplified edges.

Declaration

public double SmoothWeight { get; set; }

Property Value

Type	Description
double

Methods

| Edit this page View Source

Simplify(Geometry[], double)

Simplifies the boundaries of a set of polygonal geometries forming a coverage, preserving the coverage topology.

Declaration

public static Geometry[] Simplify(Geometry[] coverage, double tolerance)

Parameters

Type	Name	Description
Geometry[]	coverage	A set of polygonal geometries forming a coverage
double	tolerance	The simplification tolerance

Returns

Type	Description
Geometry[]	The simplified coverage polygons

| Edit this page View Source

Simplify(Geometry[], double[])

Simplifies the boundaries of a set of polygonal geometries forming a coverage, preserving the coverage topology, using a separate tolerance for each element of the coverage. Coverage edges are simplified using the lowest tolerance of each adjacent element.

Declaration

public static Geometry[] Simplify(Geometry[] coverage, double[] tolerances)

Parameters

Type	Name	Description
Geometry[]	coverage	A set of polygonal geometries forming a coverage
double[]	tolerances	The simplification tolerances (one per input element)

Returns

Type	Description
Geometry[]	The simplified coverage polygons

| Edit this page View Source

Simplify(double)

Computes the simplified coverage using a single distance tolerance, preserving the coverage topology.

Declaration

public Geometry[] Simplify(double tolerance)

Parameters

Type	Name	Description
double	tolerance	The simplification distance tolerance

Returns

Type	Description
Geometry[]	The simplified coverage polygons

| Edit this page View Source

Simplify(double, double)

Computes the simplified coverage using separate distance tolerances for inner and outer edges, preserving the coverage topology.

Declaration

public Geometry[] Simplify(double toleranceInner, double toleranceOuter)

Parameters

Type	Name	Description
double	toleranceInner	The distance tolerance for inner edges
double	toleranceOuter	The distance tolerance for outer edges

Returns

Type	Description
Geometry[]	The simplified coverage polygons

| Edit this page View Source

Simplify(double[])

Computes the simplified coverage using separate distance tolerances for each coverage element, preserving the coverage topology.

Declaration

public Geometry[] Simplify(double[] tolerances)

Parameters

Type	Name	Description
double[]	tolerances	the distance tolerances for the coverage elements

Returns

Type	Description
Geometry[]	The simplified coverage polygons

| Edit this page View Source

SimplifyInner(Geometry[], double)

Simplifies the inner boundaries of a set of polygonal geometries forming a coverage, preserving the coverage topology. Edges which form the exterior boundary of the coverage are left unchanged.

Declaration

public static Geometry[] SimplifyInner(Geometry[] coverage, double tolerance)

Parameters

Type	Name	Description
Geometry[]	coverage	A set of polygonal geometries forming a coverage
double	tolerance	The simplification tolerance

Returns

Type	Description
Geometry[]	The simplified coverage polygons

| Edit this page View Source

SimplifyOuter(Geometry[], double)

Simplifies the outer boundaries of a set of polygonal geometries forming a coverage, preserving the coverage topology. Edges in the interior of the coverage are left unchanged.

Declaration

public static Geometry[] SimplifyOuter(Geometry[] coverage, double tolerance)

Parameters

Type	Name	Description
Geometry[]	coverage	A set of polygonal geometries forming a coverage
double	tolerance	The simplification tolerance

Returns

Type	Description
Geometry[]	The simplified coverage polygons