/// <summary>
/// Gets the union of the input geometries.
/// If no input geometries were provided but a <see cref="IGeometryFactory"/> was provided,
/// an empty <see cref="IGeometryCollection"/> is returned.
/// <para/>Otherwise, the return value is <c>null</c>
/// </summary>
/// <returns>
/// A Geometry containing the union
/// or an empty <see cref="IGeometryCollection"/> if no geometries were provided in the input,
/// or <c>null</c> if not GeometryFactory was provided
/// </returns>
public IGeometry Union()
{
if (_geomFact == null)
{
return(null);
}
/**
* For points and lines, only a single union operation is
* required, since the OGC model allows self-intersecting
* MultiPoint and MultiLineStrings.
* This is not the case for polygons, so Cascaded Union is required.
*/
IGeometry unionPoints = null;
if (_points.Count > 0)
{
var ptGeom = _geomFact.BuildGeometry(_points);
unionPoints = UnionNoOpt(ptGeom);
}
IGeometry unionLines = null;
if (_lines.Count > 0)
{
var lineGeom = _geomFact.BuildGeometry(_lines);
unionLines = UnionNoOpt(lineGeom);
}
IGeometry unionPolygons = null;
if (_polygons.Count > 0)
{
unionPolygons = CascadedPolygonUnion.Union(_polygons);
}
/*
* Performing two unions is somewhat inefficient,
* but is mitigated by unioning lines and points first
*/
var unionLA = UnionWithNull(unionLines, unionPolygons);
IGeometry union;
if (unionPoints == null)
{
union = unionLA;
}
else if (unionLA == null)
{
union = unionPoints;
}
else
{
union = PointGeometryUnion.Union((IPuntal)unionPoints, unionLA);
}
if (union == null)
{
return(_geomFact.CreateGeometryCollection());
}
return(union);
}
/// <summary>
/// Computes the union of a <see cref="Point"/> geometry with
/// another arbitrary <see cref="Geometry"/>.
/// Does not copy any component geometries.
/// </summary>
/// <param name="pointGeom"></param>
/// <param name="otherGeom"></param>
/// <returns></returns>
public static Geometry Union(IPuntal pointGeom, Geometry otherGeom)
{
var unioner = new PointGeometryUnion(pointGeom, otherGeom);
return(unioner.Union());
}
///<summary>
/// Computes the union of a <see cref="IPoint"/> geometry with
/// another arbitrary <see cref="IGeometry"/>.
/// Does not copy any component geometries.
///</summary>
///<param name="pointGeom"></param>
///<param name="otherGeom"></param>
///<returns></returns>
public static IGeometry Union(IPuntal pointGeom, IGeometry otherGeom)
{
var unioner = new PointGeometryUnion(pointGeom, otherGeom);
return unioner.Union();
}
/// <summary>
/// Gets the union of the input geometries.
/// <para/>
/// The result of empty input is determined as follows:
/// <list type="Bullet">
/// <item><description>If the input is empty and a dimension can be
/// determined (i.e. an empty geometry is present),
/// an empty atomic geometry of that dimension is returned.</description></item>
/// <item><description>If no input geometries were provided but a <see cref="GeometryFactory"/> was provided,
/// an empty <see cref="GeometryCollection"/> is returned.</description></item>
/// <item><description>Otherwise, the return value is <c>null</c>.</description></item>
/// </list>
/// </summary>
/// <returns>
/// A Geometry containing the union,
/// or an empty atomic geometry, or an empty <c>GEOMETRYCOLLECTION</c>,
/// or<c>null</c> if no GeometryFactory was provided
/// </returns>
public Geometry Union()
{
if (_geomFact == null)
{
_geomFact = _extracter.Factory;
}
// Case 3
if (_geomFact == null)
{
return(null);
}
// Case 1 & 2
if (_extracter.IsEmpty)
{
return(_geomFact.CreateEmpty(_extracter.Dimension));
}
var points = _extracter.GetExtract(Dimension.Point);
var lines = _extracter.GetExtract(Dimension.Curve);
var polygons = _extracter.GetExtract(Dimension.Surface);
/**
* For points and lines, only a single union operation is
* required, since the OGC model allows self-intersecting
* MultiPoint and MultiLineStrings.
* This is not the case for polygons, so Cascaded Union is required.
*/
Geometry unionPoints = null;
if (points.Count > 0)
{
var ptGeom = _geomFact.BuildGeometry(points);
unionPoints = UnionNoOpt(ptGeom);
}
Geometry unionLines = null;
if (lines.Count > 0)
{
var lineGeom = _geomFact.BuildGeometry(lines);
unionLines = UnionNoOpt(lineGeom);
}
Geometry unionPolygons = null;
if (polygons.Count > 0)
{
unionPolygons = CascadedPolygonUnion.Union(polygons);
}
/*
* Performing two unions is somewhat inefficient,
* but is mitigated by unioning lines and points first
*/
var unionLA = UnionWithNull(unionLines, unionPolygons);
Geometry union;
if (unionPoints == null)
{
union = unionLA;
}
else if (unionLA == null)
{
union = unionPoints;
}
else
{
union = PointGeometryUnion.Union((IPuntal)unionPoints, unionLA);
}
if (union == null)
{
return(_geomFact.CreateGeometryCollection());
}
return(union);
}
