org.apache.commons.math3.geometry.euclidean.twod

## Class PolygonsSet

- java.lang.Object
- - org.apache.commons.math3.geometry.partitioning.AbstractRegion<Euclidean2D,Euclidean1D>
  - - org.apache.commons.math3.geometry.euclidean.twod.PolygonsSet

All Implemented Interfaces:
  Region<Euclidean2D>

    public class PolygonsSet
    extends AbstractRegion<Euclidean2D,Euclidean1D>

This class represents a 2D region: a set of polygons.

Since:
  3.0
Version:
  $Id: PolygonsSet.java 1422195 2012-12-15 06:45:18Z psteitz $

### Nested Class Summary

Nested Classes
`private static class` `PolygonsSet.ComparableSegment` Private extension of Segment allowing comparison.
`private static class` `PolygonsSet.Edge` Internal class for holding edges while they are processed to build a BSP tree.
`private static class` `PolygonsSet.SegmentsBuilder` Visitor building segments.
`private static class` `PolygonsSet.Vertex` Internal class for holding vertices while they are processed to build a BSP tree.

### Nested classes/interfaces inherited from interface org.apache.commons.math3.geometry.partitioning.Region

`Region.Location`

### Field Summary

Fields
`private Vector2D[][]` `vertices` Vertices organized as boundary loops.

### Constructor Summary

Constructors
Constructor and Description
`PolygonsSet()` Build a polygons set representing the whole real line.
`PolygonsSet(BSPTree<Euclidean2D> tree)` Build a polygons set from a BSP tree.
`PolygonsSet(Collection<SubHyperplane<Euclidean2D>> boundary)` Build a polygons set from a Boundary REPresentation (B-rep).
`PolygonsSet(double xMin, double xMax, double yMin, double yMax)` Build a parallellepipedic box.
`PolygonsSet(double hyperplaneThickness, Vector2D... vertices)` Build a polygon from a simple list of vertices.

### Method Summary

Methods
`private static Line[]` `boxBoundary(double xMin, double xMax, double yMin, double yMax)` Create a list of hyperplanes representing the boundary of a box.
`PolygonsSet` `buildNew(BSPTree<Euclidean2D> tree)` Build a region using the instance as a prototype.
`protected void` `computeGeometricalProperties()` Compute some geometrical properties.
`private List<PolygonsSet.ComparableSegment>` `followLoop(AVLTree.Node node, AVLTree<PolygonsSet.ComparableSegment> sorted)` Follow a boundary loop.
`Vector2D[][]` `getVertices()` Get the vertices of the polygon.
`private static void` `insertEdges(double hyperplaneThickness, BSPTree<Euclidean2D> node, List<PolygonsSet.Edge> edges)` Recursively build a tree by inserting cut sub-hyperplanes.
`private static BSPTree<Euclidean2D>` `verticesToTree(double hyperplaneThickness, Vector2D... vertices)` Build the BSP tree of a polygons set from a simple list of vertices.

### Methods inherited from class org.apache.commons.math3.geometry.partitioning.AbstractRegion

`applyTransform, checkPoint, checkPoint, contains, copySelf, getBarycenter, getBoundarySize, getSize, getTree, intersection, isEmpty, isEmpty, setBarycenter, setSize, side`

### Methods inherited from class java.lang.Object

`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

### Field Detail

#### vertices

    private Vector2D[][] vertices

Vertices organized as boundary loops.

### Constructor Detail

#### PolygonsSet

    public PolygonsSet()

Build a polygons set representing the whole real line.

#### PolygonsSet

    public PolygonsSet(BSPTree<Euclidean2D> tree)

Build a polygons set from a BSP tree.

The leaf nodes of the BSP tree must have a `Boolean` attribute representing the inside status of the corresponding cell (true for inside cells, false for outside cells). In order to avoid building too many small objects, it is recommended to use the predefined constants `Boolean.TRUE` and `Boolean.FALSE`

Parameters:
  `tree` - inside/outside BSP tree representing the region

#### PolygonsSet

    public PolygonsSet(Collection<SubHyperplane<Euclidean2D>> boundary)

Build a polygons set from a Boundary REPresentation (B-rep).

The boundary is provided as a collection of `sub-hyperplanes`. Each sub-hyperplane has the interior part of the region on its minus side and the exterior on its plus side.

The boundary elements can be in any order, and can form several non-connected sets (like for example polygons with holes or a set of disjoint polyhedrons considered as a whole). In fact, the elements do not even need to be connected together (their topological connections are not used here). However, if the boundary does not really separate an inside open from an outside open (open having here its topological meaning), then subsequent calls to the `checkPoint` method will not be meaningful anymore.

If the boundary is empty, the region will represent the whole space.

Parameters:
  `boundary` - collection of boundary elements, as a collection of `SubHyperplane` objects

#### PolygonsSet

    public PolygonsSet(double xMin,
               double xMax,
               double yMin,
               double yMax)

Build a parallellepipedic box.

Parameters:
  `xMin` - low bound along the x direction
  `xMax` - high bound along the x direction
  `yMin` - low bound along the y direction
  `yMax` - high bound along the y direction

#### PolygonsSet

    public PolygonsSet(double hyperplaneThickness,
               Vector2D... vertices)

Build a polygon from a simple list of vertices.

The boundary is provided as a list of points considering to represent the vertices of a simple loop. The interior part of the region is on the left side of this path and the exterior is on its right side.

This constructor does not handle polygons with a boundary forming several disconnected paths (such as polygons with holes).

For cases where this simple constructor applies, it is expected to be numerically more robust than the `general constructor` using `subhyperplanes`.

If the list is empty, the region will represent the whole space.

Polygons with thin pikes or dents are inherently difficult to handle because they involve lines with almost opposite directions at some vertices. Polygons whose vertices come from some physical measurement with noise are also difficult because an edge that should be straight may be broken in lots of different pieces with almost equal directions. In both cases, computing the lines intersections is not numerically robust due to the almost 0 or almost π angle. Such cases need to carefully adjust the `hyperplaneThickness` parameter. A too small value would often lead to completely wrong polygons with large area wrongly identified as inside or outside. Large values are often much safer. As a rule of thumb, a value slightly below the size of the most accurate detail needed is a good value for the `hyperplaneThickness` parameter.

Parameters:
  `hyperplaneThickness` - tolerance below which points are considered to belong to the hyperplane (which is therefore more a slab)
  `vertices` - vertices of the simple loop boundary
Since:
  3.1

### Method Detail

#### boxBoundary

    private static Line[] boxBoundary(double xMin,
                     double xMax,
                     double yMin,
                     double yMax)

Create a list of hyperplanes representing the boundary of a box.

Parameters:
  `xMin` - low bound along the x direction
  `xMax` - high bound along the x direction
  `yMin` - low bound along the y direction
  `yMax` - high bound along the y direction
Returns:
  boundary of the box

#### verticesToTree

    private static BSPTree<Euclidean2D> verticesToTree(double hyperplaneThickness,
                                      Vector2D... vertices)

Build the BSP tree of a polygons set from a simple list of vertices.

The boundary is provided as a list of points considering to represent the vertices of a simple loop. The interior part of the region is on the left side of this path and the exterior is on its right side.

This constructor does not handle polygons with a boundary forming several disconnected paths (such as polygons with holes).

For cases where this simple constructor applies, it is expected to be numerically more robust than the `general constructor` using `subhyperplanes`.

Parameters:
  `hyperplaneThickness` - tolerance below which points are consider to belong to the hyperplane (which is therefore more a slab)
  `vertices` - vertices of the simple loop boundary
Returns:
  the BSP tree of the input vertices

#### insertEdges

    private static void insertEdges(double hyperplaneThickness,
                   BSPTree<Euclidean2D> node,
                   List<PolygonsSet.Edge> edges)

Recursively build a tree by inserting cut sub-hyperplanes.

Parameters:
  `hyperplaneThickness` - tolerance below which points are consider to belong to the hyperplane (which is therefore more a slab)
  `node` - current tree node (it is a leaf node at the beginning of the call)
  `edges` - list of edges to insert in the cell defined by this node (excluding edges not belonging to the cell defined by this node)

#### buildNew

    public PolygonsSet buildNew(BSPTree<Euclidean2D> tree)

Build a region using the instance as a prototype.

This method allow to create new instances without knowing exactly the type of the region. It is an application of the prototype design pattern.

The leaf nodes of the BSP tree must have a `Boolean` attribute representing the inside status of the corresponding cell (true for inside cells, false for outside cells). In order to avoid building too many small objects, it is recommended to use the predefined constants `Boolean.TRUE` and `Boolean.FALSE`. The tree also must have either null internal nodes or internal nodes representing the boundary as specified in the `getTree` method).

Specified by:
  `buildNew` in interface `Region<Euclidean2D>`
Specified by:
  `buildNew` in class `AbstractRegion<Euclidean2D,Euclidean1D>`
Parameters:
  `tree` - inside/outside BSP tree representing the new region
Returns:
  the built region

#### computeGeometricalProperties

    protected void computeGeometricalProperties()

Compute some geometrical properties.

The properties to compute are the barycenter and the size.

Specified by:
  `computeGeometricalProperties` in class `AbstractRegion<Euclidean2D,Euclidean1D>`

#### getVertices

    public Vector2D[][] getVertices()

Get the vertices of the polygon.

The polygon boundary can be represented as an array of loops, each loop being itself an array of vertices.

In order to identify open loops which start and end by infinite edges, the open loops arrays start with a null point. In this case, the first non null point and the last point of the array do not represent real vertices, they are dummy points intended only to get the direction of the first and last edge. An open loop consisting of a single infinite line will therefore be represented by a three elements array with one null point followed by two dummy points. The open loops are always the first ones in the loops array.

If the polygon has no boundary at all, a zero length loop array will be returned.

All line segments in the various loops have the inside of the region on their left side and the outside on their right side when moving in the underlying line direction. This means that closed loops surrounding finite areas obey the direct trigonometric orientation.

Returns:
  vertices of the polygon, organized as oriented boundary loops with the open loops first (the returned value is guaranteed to be non-null)

#### followLoop

    private List<PolygonsSet.ComparableSegment> followLoop(AVLTree.Node node,
                                                 AVLTree<PolygonsSet.ComparableSegment> sorted)

Follow a boundary loop.

Parameters:
  `node` - node containing the segment starting the loop
  `sorted` - set of segments belonging to the boundary, sorted by start points (contains `node`)
Returns:
  a list of connected sub-hyperplanes starting at `node`