/// <summary>
/// Computes the union of
/// a collection of <see cref="Geometry"/>s.
/// </summary>
/// <param name="polys">A collection of <see cref="IPolygonal"/> <see cref="Geometry"/>s.</param>
/// <returns></returns>
public static Geometry Union(ICollection <Geometry> polys)
{
var op = new CascadedPolygonUnion(polys);
return(op.Union());
}
/// <summary>
/// Gets the union of the input geometries.
/// If no input geometries were provided but a <see cref="GeometryFactory"/> was provided,
/// an empty <see cref="GeometryCollection"/> is returned.
/// <para/>Otherwise, the return value is <c>null</c>
/// </summary>
/// <returns>
/// A Geometry containing the union
/// or an empty <see cref="GeometryCollection"/> if no geometries were provided in the input,
/// or <c>null</c> if not GeometryFactory was provided
/// </returns>
public Geometry 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.
*/
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);
}