public Segment Intersection(Segment segment) { // if either segment is empty, the intersection is also empty if (IsEmpty || segment.IsEmpty) { return(Empty); } // if the segments are equal, just return a new equal segment if (this == segment) { return(new Segment(_p1, _p2, IsP1Excluded, IsP2Excluded)); } // if either segment is a Point, just see if the point is contained in the other segment if (IsPoint) { return(segment.Contains(_p1) ? new Segment(_p1) : Empty); } if (segment.IsPoint) { return(Contains(segment._p1) ? new Segment(segment._p1) : Empty); } // okay, no easy answer, so let's do the math... var p1 = _p1; var v1 = _p2 - _p1; var p2 = segment._p1; var v2 = segment._p2 - segment._p1; var endpointVector = p2 - p1; var xProd = Vector.CrossProduct(v1, v2); // if segments are not parallel, then look for intersection on each segment if (!DoubleHelper.AreVirtuallyEqual(Slope, segment.Slope)) { // check for intersection on other segment var s = Vector.CrossProduct(endpointVector, v1) / xProd; if (s < 0 || s > 1) { return(Empty); } // check for intersection on this segment s = Vector.CrossProduct(endpointVector, v2) / xProd; if (s < 0 || s > 1) { return(Empty); } // intersection of segments is a point return(new Segment(p1 + s * v1)); } // segments are parallel xProd = Vector.CrossProduct(endpointVector, v1); if (xProd * xProd > 1.0e-06 * v1.LengthSquared * endpointVector.LengthSquared) { // segments do not intersect return(Empty); } // intersection is overlapping segment var result = new Segment(); // to determine the overlapping segment, create reference segments where the endpoints are *not* excluded var refThis = new Segment(_p1, _p2); var refSegment = new Segment(segment._p1, segment._p2); // check whether this segment is contained in the other segment var includeThisP1 = refSegment.Contains(refThis._p1); var includeThisP2 = refSegment.Contains(refThis._p2); if (includeThisP1 && includeThisP2) { result._p1 = _p1; result._p2 = _p2; result.IsP1Excluded = IsP1Excluded || !segment.Contains(_p1); result.IsP2Excluded = IsP2Excluded || !segment.Contains(_p2); return(result); } // check whether the other segment is contained in this segment var includeSegmentP1 = refThis.Contains(refSegment._p1); var includeSegmentP2 = refThis.Contains(refSegment._p2); if (includeSegmentP1 && includeSegmentP2) { result._p1 = segment._p1; result._p2 = segment._p2; result.IsP1Excluded = segment.IsP1Excluded || !Contains(segment._p1); result.IsP2Excluded = segment.IsP2Excluded || !Contains(segment._p2); return(result); } // the intersection must include one endpoint from this segment and one endpoint from the other segment if (includeThisP1) { result._p1 = _p1; result.IsP1Excluded = IsP1Excluded || !segment.Contains(_p1); } else { result._p1 = _p2; result.IsP1Excluded = IsP2Excluded || !segment.Contains(_p2); } if (includeSegmentP1) { result._p2 = segment._p1; result.IsP2Excluded = segment.IsP1Excluded || !Contains(segment._p1); } else { result._p2 = segment._p2; result.IsP2Excluded = segment.IsP2Excluded || !Contains(segment._p2); } return(result); }