/// <summary>
/// Computes a <c>Geometry</c> representing the point-set
/// which is contained in both input <c>Geometry</c>s .
/// </summary>
/// <param name="a">The 1st <c>Geometry</c></param>
/// <param name="b">The 2nd <c>Geometry</c></param>
/// <returns>A point-set combining the points of
/// <c>Geometry</c>'s <c>a</c> and <c>b</c>.
/// </returns>
/// <seealso cref="Geometry.Union(Geometry)"/>
public virtual Geometry Union(Geometry a, Geometry b)
{
// handle empty geometry cases
if (a.IsEmpty || (b == null || b.IsEmpty))
{
// both empty - check dimensions
if (a.IsEmpty && (b == null || b.IsEmpty))
{
return(OverlayOp.CreateEmptyResult(SpatialFunction.Union, a, b, a.Factory));
}
// special case: if either input is empty ==> result = other arg
if (a.IsEmpty)
{
return(b.Copy());
}
if (b == null || b.IsEmpty)
{
return(a.Copy());
}
}
// TODO: optimize if envelopes of geometries do not intersect
CheckNotGeometryCollection(a, b);
return(Overlay(a, b, SpatialFunction.Union));
}
/// <summary>
/// Computes a <c>Geometry</c> representing the closure of the point-set
/// which is the union of the points in <c>Geometry</c> <c>a</c> which are not
/// contained in the Geometry <c>b</c>,
/// with the points in the <c>b</c> Geometry not contained in the <c>Geometry</c> <c>a</c>.
/// </summary>
/// <param name="a">The 1st <c>Geometry</c></param>
/// <param name="b">The 2nd <c>Geometry</c></param>
/// <returns>
/// A Geometry representing the point-set symmetric difference
/// of <c>Geometry</c>'s <c>a</c> and <c>b</c>.
/// </returns>
/// <seealso cref="Geometry.SymmetricDifference(Geometry)"/>
public virtual Geometry SymmetricDifference(Geometry a, Geometry b)
{
// handle empty geometry cases
if (a.IsEmpty || (b == null || b.IsEmpty))
{
// both empty - check dimensions
if (a.IsEmpty && (b == null || b.IsEmpty))
{
return(OverlayOp.CreateEmptyResult(SpatialFunction.SymDifference, a, b, a.Factory));
}
// special case: if either input is empty ==> result = other arg
if (a.IsEmpty)
{
return(b.Copy());
}
if (b == null || b.IsEmpty)
{
return(a.Copy());
}
}
CheckNotGeometryCollection(a, b);
return(Overlay(a, b, SpatialFunction.SymDifference));
}
/// <summary>
/// Computes a <c>Geometry</c> representing the point-set which is
/// common to both <c>a</c> and <c>b</c> Geometry.
/// </summary>
/// <param name="a">The 1st <c>Geometry</c></param>
/// <param name="b">The 2nd <c>Geometry</c></param>
/// <returns>A geometry representing the point-set common to the two <c>Geometry</c>s.</returns>
/// <seealso cref="Geometry.Intersection"/>
public virtual Geometry Intersection(Geometry a, Geometry b)
{
/**
* TODO: MD - add optimization for P-A case using Point-In-Polygon
*/
// special case: if one input is empty ==> empty
if (a.IsEmpty || b.IsEmpty)
{
return(OverlayOp.CreateEmptyResult(SpatialFunction.Intersection, a, b, a.Factory));
}
// compute for GCs
// (An inefficient algorithm, but will work)
// TODO: improve efficiency of computation for GCs
if (a.OgcGeometryType == OgcGeometryType.GeometryCollection)
{
var g2 = b;
return(GeometryCollectionMapper.Map(
(GeometryCollection)a, g => g.Intersection(g2)));
}
// No longer needed since GCs are handled by previous code
//CheckNotGeometryCollection(a, b);
return(Overlay(a, b, SpatialFunction.Intersection));
}
/// <summary>
/// Computes a <c>Geometry</c> representing the closure of the point-set
/// of the points contained in this <c>Geometry</c> that are not contained in
/// the <c>other</c> Geometry.
/// </summary>
/// <param name="a">The 1st <c>Geometry</c></param>
/// <param name="b">The 2nd <c>Geometry</c></param>
/// <returns>
/// A Geometry representing the point-set difference
/// of <c>Geometry</c>'s <c>a</c> and <c>b</c>.
/// </returns>
/// <seealso cref="Geometry.Difference(Geometry)"/>
public virtual Geometry Difference(Geometry a, Geometry b)
{
// special case: if A.isEmpty ==> empty; if B.isEmpty ==> A
if (a.IsEmpty)
{
return(OverlayOp.CreateEmptyResult(SpatialFunction.Difference, a, b, a.Factory));
}
if (b == null || b.IsEmpty)
{
return(a.Copy());
}
CheckNotGeometryCollection(a, b);
return(Overlay(a, b, SpatialFunction.Difference));
}