/// <summary>
///
/// </summary>
/// <returns></returns>
public virtual IntersectionMatrix ComputeIM()
{
IntersectionMatrix im = new IntersectionMatrix();
// since Geometries are finite and embedded in a 2-D space, the EE element must always be 2
im.Set(Locations.Exterior, Locations.Exterior, Dimensions.Surface);
// if the Geometries don't overlap there is nothing to do
if (!arg[0].Geometry.EnvelopeInternal.Intersects(arg[1].Geometry.EnvelopeInternal))
{
ComputeDisjointIM(im);
return im;
}
arg[0].ComputeSelfNodes(li, false);
arg[1].ComputeSelfNodes(li, false);
// compute intersections between edges of the two input geometries
SegmentIntersector intersector = arg[0].ComputeEdgeIntersections(arg[1], li, false);
ComputeIntersectionNodes(0);
ComputeIntersectionNodes(1);
/*
* Copy the labelling for the nodes in the parent Geometries. These override
* any labels determined by intersections between the geometries.
*/
CopyNodesAndLabels(0);
CopyNodesAndLabels(1);
// complete the labelling for any nodes which only have a label for a single point
LabelIsolatedNodes();
// If a proper intersection was found, we can set a lower bound on the IM.
ComputeProperIntersectionIM(intersector, im);
/*
* Now process improper intersections
* (eg where one or other of the geometries has a vertex at the intersection point)
* We need to compute the edge graph at all nodes to determine the IM.
*/
// build EdgeEnds for all intersections
EdgeEndBuilder eeBuilder = new EdgeEndBuilder();
IList ee0 = eeBuilder.ComputeEdgeEnds(arg[0].GetEdgeEnumerator());
InsertEdgeEnds(ee0);
IList ee1 = eeBuilder.ComputeEdgeEnds(arg[1].GetEdgeEnumerator());
InsertEdgeEnds(ee1);
LabelNodeEdges();
/*
* Compute the labeling for isolated components
* <br>
* Isolated components are components that do not touch any other components in the graph.
* They can be identified by the fact that they will
* contain labels containing ONLY a single element, the one for their parent point.
* We only need to check components contained in the input graphs, since
* isolated components will not have been replaced by new components formed by intersections.
*/
LabelIsolatedEdges(0, 1);
LabelIsolatedEdges(1, 0);
// update the IM from all components
UpdateIM(im);
return im;
}
/// <summary>
/// If the Geometries are disjoint, we need to enter their dimension and
/// boundary dimension in the Ext rows in the IM
/// </summary>
/// <param name="im"></param>
private void ComputeDisjointIM(IntersectionMatrix im)
{
IGeometry ga = arg[0].Geometry;
if (!ga.IsEmpty)
{
im.Set(Locations.Interior, Locations.Exterior, ga.Dimension);
im.Set(Locations.Boundary, Locations.Exterior, ga.BoundaryDimension);
}
IGeometry gb = arg[1].Geometry;
if (!gb.IsEmpty)
{
im.Set(Locations.Exterior, Locations.Interior, gb.Dimension);
im.Set(Locations.Exterior, Locations.Boundary, gb.BoundaryDimension);
}
}
