/// <summary>
/// check whether two linear segments intersect on the plane
/// </summary>
/// <param name="seg1"></param>
/// <param name="seg2"></param>
/// <returns></returns>
public static bool CheckSegmentIntersection(Segment seg1, Segment seg2)
{
bool isSameSide1 = CheckPointOnSameSide(seg1, seg2);
bool isSameSide2 = CheckPointOnSameSide(seg2, seg1);
return (!isSameSide1) & (!isSameSide2);
}
/// <summary>
/// Basic sample for intersec / Not-intersec
/// ([1.0, 2.0], [2.0, 3.0]) ([1.0, 1.0], [2.0, 2.0]) - false
/// ([1.0, 2.0], [2.0, 2.0]) ([1.0, 1.0], [2.0, 3.0]) - ture
///
/// one segment is vertical , other segment is random (vertical, horizontal ...)
/// ([0,0], [0,2]) ([1,1], [1,3]) - false
/// ([0,0], [0,2]) ([0,-2], [0,5]) - true
/// ([0,0], [0,2]) ([0,-2], [1,3]) - false
/// ([0,0], [0,2]) ([0, 1], [1,3]) - true
///
/// one segment is horizontal , other segment is random (vertical, horizontal ...)
/// ([0,0], [2,0]) ([1,1], [2,3] -false
/// ([0,0], [2,0]) ([-2,0], [5,0]) - true
/// ([0,0], [2,0]) ([-2,0], [1,3]) - false
/// ([0,0], [2,0]) ([1,0], [1,3]) - true
///
/// segment is just a point, the other is random (point, pass the point ...)
/// ([0,0], [0,0]) ([1,1], [2,3] -false
/// ([0,0], [0,0]) ([-1,1], [1,1] -true
/// ([0,0], [0,0]) ([1,1], [2,2] -true
/// ([0,0], [0,0]) ([1,1], [1,1] -false
///
/// </summary>
static void TestSegmentIntersec()
{
Segment seg1 = new Segment
{
P1 = new Point { X = 0.0, Y = 0.0 },
P2 = new Point { X = 2.0, Y = 0.0 }
};
Segment seg2 = new Segment
{
P1 = new Point { X = 1.0, Y = 1.0},
P2 = new Point { X = 1.0, Y = 3.0}
};
Console.WriteLine(Algorithm.CheckSegmentIntersection(seg1, seg2));
}
/// <summary>
/// check the points on targetSeg is on the same side of a segment
/// </summary>
/// <param name="seg"></param>
/// <param name="targetSeg"></param>
/// <returns></returns>
private static bool CheckPointOnSameSide(Segment seg, Segment targetSeg)
{
PointLocation location1 = CheckPointLocation(seg, targetSeg.P1);
PointLocation location2 = CheckPointLocation(seg, targetSeg.P2);
return Convert.ToBoolean(location1 & location2);
}
/// <summary>
/// Check point location toward a segment
/// </summary>
/// <param name="seg"></param>
/// <param name="point"></param>
/// <returns></returns>
private static PointLocation CheckPointLocation(Segment seg, Point point)
{
double yValue = 0.0;
if ((seg.Slope != null) && (seg.Intercept != null))
{
yValue = (double)seg.Slope * point.X + (double)seg.Intercept;
if (point.Y > yValue)
return PointLocation.Above;
else
if (point.Y == yValue)
return PointLocation.OnSeg;
else
return PointLocation.Below;
}
else
{
if (point.X == seg.P1.X)
{
if (point.Y > Math.Max(seg.P2.Y, seg.P1.Y))
return PointLocation.Above;
else
if (point.Y < Math.Min(seg.P2.Y, seg.P1.Y))
return PointLocation.Below;
else
return PointLocation.OnSeg;
}
else
{
return (point.X > seg.P1.X) ? PointLocation.Below : PointLocation.Above;
}
}
}
