/// <summary>
/// Calculates the intersection between two 2D segments.
/// </summary>
/// <param name="segment1">The first 2D segment.</param>
/// <param name="segment2">The second 2D segment.</param>
/// <returns>The intersection calculation result.</returns>
/// <exception cref="ArgumentNullException">Thrown when <paramref name="segment1"/> or
/// <paramref name="segment2"/> is <c>null</c>.</exception>
/// <remarks>Implementation from http://geomalgorithms.com/a05-_intersect-1.html
/// based on method <c>intersect2D_2Segments</c>.</remarks>
public static Segment2DIntersectSegment2DResult GetIntersectionBetweenSegments(Segment2D segment1, Segment2D segment2)
{
if (segment1 == null)
{
throw new ArgumentNullException(nameof(segment1));
}
if (segment2 == null)
{
throw new ArgumentNullException(nameof(segment2));
}
Vector <double> u = segment1.SecondPoint - segment1.FirstPoint;
Vector <double> v = segment2.SecondPoint - segment2.FirstPoint;
Vector <double> w = segment1.FirstPoint - segment2.FirstPoint;
double d = PerpDotProduct(u, v);
if (Math.Abs(d) < epsilonForComparisons)
{
// Segments can be considered parallel...
if (AreCollinear(u, v, w))
{
// ... and collinear ...
if (IsSegmentAsPointIntersectionDegenerateScenario(segment1, segment2))
{
// ... but either or both segments are point degenerates:
return(HandleSegmentAsPointIntersectionDegenerates(segment1, segment2));
}
// ... so there is a possibility of overlapping or connected lines:
return(HandleCollinearSegmentIntersection(segment1, segment2, v, w));
}
// ... but not collinear, so no intersection possible:
return(Segment2DIntersectSegment2DResult.CreateNoIntersectResult());
}
// Segments are at an angle and may intersect:
double sI = PerpDotProduct(v, w) / d;
if (sI < 0.0 || sI > 1.0)
{
return(Segment2DIntersectSegment2DResult.CreateNoIntersectResult());
}
double tI = PerpDotProduct(u, w) / d;
if (tI < 0.0 || tI > 1.0)
{
return(Segment2DIntersectSegment2DResult.CreateNoIntersectResult());
}
Point2D intersectionPoint = segment1.FirstPoint + u.Multiply(sI);
return(Segment2DIntersectSegment2DResult.CreateIntersectionResult(intersectionPoint));
}
private static Segment2DIntersectSegment2DResult HandleCollinearSegmentIntersection(Segment2D segment1, Segment2D segment2, Vector <double> v, Vector <double> w)
{
double t0, t1;
Vector <double> w2 = segment1.SecondPoint - segment2.FirstPoint;
if (Math.Abs(v[0]) > double.Epsilon)
{
t0 = w[0] / v[0];
t1 = w2[0] / v[0];
}
else
{
t0 = w[1] / v[1];
t1 = w2[1] / v[1];
}
// Require t0 to be smaller than t1, swapping if needed:
if (t0 > t1)
{
double tempSwapVariable = t0;
t0 = t1;
t1 = tempSwapVariable;
}
if (t0 > 1.0 || t1 < 0.0)
{
// There is no overlap:
return(Segment2DIntersectSegment2DResult.CreateNoIntersectResult());
}
t0 = Math.Max(0.0, t0);
t1 = Math.Min(1.0, t1);
Point2D intersectionPoint1 = segment2.FirstPoint + v.Multiply(t0);
if (Math.Abs(t0 - t1) < epsilonForComparisons)
{
// Segments intersect at a point:
return(Segment2DIntersectSegment2DResult.CreateIntersectionResult(intersectionPoint1));
}
// Segments overlap:
Point2D intersectionPoint2 = segment2.FirstPoint + v.Multiply(t1);
return(Segment2DIntersectSegment2DResult.CreateOverlapResult(intersectionPoint1, intersectionPoint2));
}
private static Segment2DIntersectSegment2DResult HandleSegmentAsPointIntersectionDegenerates(Segment2D segment1, Segment2D segment2)
{
bool segment1IsPointDegenerate = IsSegmentActuallyPointDegenerate(segment1);
bool segment2IsPointDegenerate = IsSegmentActuallyPointDegenerate(segment2);
if (segment1IsPointDegenerate)
{
if (segment2IsPointDegenerate)
{
// Both segments can be considered Point2D
return(segment1.FirstPoint.Equals(segment2.FirstPoint)
? Segment2DIntersectSegment2DResult.CreateIntersectionResult(segment1.FirstPoint)
: Segment2DIntersectSegment2DResult.CreateNoIntersectResult());
}
return(IsPointInCollinearSegment(segment1.FirstPoint, segment2)
? Segment2DIntersectSegment2DResult.CreateIntersectionResult(segment1.FirstPoint)
: Segment2DIntersectSegment2DResult.CreateNoIntersectResult());
}
return(IsPointInCollinearSegment(segment2.FirstPoint, segment1)
? Segment2DIntersectSegment2DResult.CreateIntersectionResult(segment2.FirstPoint)
: Segment2DIntersectSegment2DResult.CreateNoIntersectResult());
}