public override int ComputeIntersect(Coordinate p1, Coordinate p2, Coordinate q1, Coordinate q2)
{
IsProper = false;
// first try a fast test to see if the envelopes of the lines intersect
if (!Envelope.Intersects(p1, p2, q1, q2))
{
return(NoIntersection);
}
// for each endpoint, compute which side of the other segment it lies
// if both endpoints lie on the same side of the other segment,
// the segments do not intersect
var Pq1 = Orientation.Index(p1, p2, q1);
var Pq2 = Orientation.Index(p1, p2, q2);
if ((Pq1 > 0 && Pq2 > 0) ||
(Pq1 < 0 && Pq2 < 0))
{
return(NoIntersection);
}
var Qp1 = Orientation.Index(q1, q2, p1);
var Qp2 = Orientation.Index(q1, q2, p2);
if ((Qp1 > 0 && Qp2 > 0) ||
(Qp1 < 0 && Qp2 < 0))
{
return(NoIntersection);
}
bool collinear = Pq1 == 0 && Pq2 == 0 && Qp1 == 0 && Qp2 == 0;
if (collinear)
{
return(ComputeCollinearIntersection(p1, p2, q1, q2));
}
/*
* At this point we know that there is a single intersection point
* (since the lines are not collinear).
*/
/*
* Check if the intersection is an endpoint. If it is, copy the endpoint as
* the intersection point. Copying the point rather than computing it
* ensures the point has the exact value, which is important for
* robustness. It is sufficient to simply check for an endpoint which is on
* the other line, since at this point we know that the inputLines must
* intersect.
*/
if (Pq1 == 0 || Pq2 == 0 || Qp1 == 0 || Qp2 == 0)
{
IsProper = false;
/*
* Check for two equal endpoints.
* This is done explicitly rather than by the orientation tests
* below in order to improve robustness.
*
* [An example where the orientation tests fail to be consistent is
* the following (where the true intersection is at the shared endpoint
* POINT (19.850257749638203 46.29709338043669)
*
* LINESTRING ( 19.850257749638203 46.29709338043669, 20.31970698357233 46.76654261437082 )
* and
* LINESTRING ( -48.51001596420236 -22.063180333403878, 19.850257749638203 46.29709338043669 )
*
* which used to produce the INCORRECT result: (20.31970698357233, 46.76654261437082, NaN)
*
*/
if (p1.Equals2D(q1) || p1.Equals2D(q2))
{
IntersectionPoint[0] = p1;
}
else if (p2.Equals2D(q1) || p2.Equals2D(q2))
{
IntersectionPoint[0] = p2;
}
else if (Pq1 == 0)
{
IntersectionPoint[0] = q1.Copy();
}
else if (Pq2 == 0)
{
IntersectionPoint[0] = q2.Copy();
}
else if (Qp1 == 0)
{
IntersectionPoint[0] = p1.Copy();
}
else if (Qp2 == 0)
{
IntersectionPoint[0] = p2.Copy();
}
}
else
{
IsProper = true;
IntersectionPoint[0] = Intersection(p1, p2, q1, q2);
}
return(PointIntersection);
}