/// <summary>
/// Computes a segment intersection using homogeneous coordinates.
/// Round-off error can cause the raw computation to fail,
/// (usually due to the segments being approximately parallel).
/// If this happens, a reasonable approximation is computed instead.
/// </summary>
private static Coordinate SafeHCoordinateIntersection(Coordinate p1, Coordinate p2, Coordinate q1, Coordinate q2)
{
Coordinate intPt;
try
{
intPt = HCoordinate.Intersection(p1, p2, q1, q2);
}
catch (NotRepresentableException e)
{
intPt = CentralEndpointIntersector.GetIntersection(p1, p2, q1, q2);
}
return(intPt);
}
/// <summary>
/// This method computes the actual value of the intersection point.
/// To obtain the maximum precision from the intersection calculation,
/// the coordinates are normalized by subtracting the minimum
/// ordinate values (in absolute value). This has the effect of
/// removing common significant digits from the calculation to
/// maintain more bits of precision.
/// </summary>
/// <param name="p1"></param>
/// <param name="p2"></param>
/// <param name="q1"></param>
/// <param name="q2"></param>
/// <returns></returns>
private Coordinate Intersection(Coordinate p1, Coordinate p2, Coordinate q1, Coordinate q2)
{
Coordinate intPt = IntersectionWithNormalization(p1, p2, q1, q2);
/*
* // TESTING ONLY
* var intPtDD = CGAlgorithmsDD.Intersection(p1, p2, q1, q2);
* var dist = intPt.Distance(intPtDD);
* System.Console.WriteLine(intPt + " - " + intPtDD + " dist = " + dist);
* //intPt = intPtDD;
*/
/*
* Due to rounding it can happen that the computed intersection is
* outside the envelopes of the input segments. Clearly this
* is inconsistent.
* This code checks this condition and forces a more reasonable answer
*
* MD - May 4 2005 - This is still a problem. Here is a failure case:
*
* LINESTRING (2089426.5233462777 1180182.3877339689, 2085646.6891757075 1195618.7333999649)
* LINESTRING (1889281.8148903656 1997547.0560044837, 2259977.3672235999 483675.17050843034)
* int point = (2097408.2633752143,1144595.8008114607)
*
* MD - Dec 14 2006 - This does not seem to be a failure case any longer
*/
if (!IsInSegmentEnvelopes(intPt))
{
// compute a safer result
intPt = CentralEndpointIntersector.GetIntersection(p1, p2, q1, q2);
}
if (PrecisionModel != null)
{
PrecisionModel.MakePrecise(intPt);
}
return(intPt);
}
/// <summary>
/// Computes an approximate intersection of two line segments
/// by taking the most central of the endpoints of the segments.
/// This is effective in cases where the segments are nearly parallel
/// and should intersect at an endpoint.
/// </summary>
/// <param name="p00">The 1st coordinate of the 1st line segement.</param>
/// <param name="p01">The 2nd coordinate of the 1st line segemen.</param>
/// <param name="p10">The 1st coordinate of the 2nd line segement.</param>
/// <param name="p11">The 2nd coordinate of the 2nd line segement.</param>
/// <returns></returns>
public static Coordinate GetIntersection(Coordinate p00, Coordinate p01, Coordinate p10, Coordinate p11)
{
var intor = new CentralEndpointIntersector(p00, p01, p10, p11);
return(intor.Intersection);
}
/// <summary>
/// Computes an approximate intersection of two line segments
/// by taking the most central of the endpoints of the segments.
/// This is effective in cases where the segments are nearly parallel
/// and should intersect at an endpoint.
/// </summary>
/// <param name="p00">The 1st coordinate of the 1st line segement.</param>
/// <param name="p01">The 2nd coordinate of the 1st line segemen.</param>
/// <param name="p10">The 1st coordinate of the 2nd line segement.</param>
/// <param name="p11">The 2nd coordinate of the 2nd line segement.</param>
/// <returns></returns>
public static Coordinate GetIntersection(Coordinate p00, Coordinate p01, Coordinate p10, Coordinate p11)
{
var intor = new CentralEndpointIntersector(p00, p01, p10, p11);
return intor.Intersection;
}
