/// <summary>
/// Uses the intersection count to detect if there is an intersection
/// </summary>
/// <param name="other"></param>
/// <returns></returns>
public bool Intersects(Segment other)
{
return (IntersectionCount(other) > 0);
}
/// <summary>
/// Determines the shortest distance between two segments
/// </summary>
/// <param name="lineSegment">Segment, The line segment to test against this segment</param>
/// <returns>Double, the shortest distance between two segments</returns>
public double DistanceTo(Segment lineSegment)
{
//http://www.geometryalgorithms.com/Archive/algorithm_0106/algorithm_0106.htm
const double smallNum = 0.00000001;
Vector u = ToVector(); // Segment 1
Vector v = lineSegment.ToVector(); // Segment 2
Vector w = ToVector();
double a = u.Dot(u); // length of segment 1
double b = u.Dot(v); // length of segment 2 projected onto line 1
double c = v.Dot(v); // length of segment 2
double d = u.Dot(w); //
double e = v.Dot(w);
double dist = a * c - b * b;
double sc, sN, sD = dist;
double tc, tN, tD = dist;
// compute the line parameters of the two closest points
if (dist < smallNum)
{
// the lines are almost parallel force using point P0 on segment 1
// to prevent possible division by 0 later
sN = 0.0;
sD = 1.0;
tN = e;
tD = c;
}
else
{
// get the closest points on the infinite lines
sN = (b * e - c * d);
tN = (a * e - b * d);
if (sN < 0.0)
{
// sc < 0 => the s=0 edge is visible
sN = 0.0;
tN = e;
tD = c;
}
else if (sN > sD)
{
// sc > 1 => the s=1 edge is visible
sN = sD;
tN = e + b;
tD = c;
}
}
if (tN < 0.0)
{
// tc < 0 => the t=0 edge is visible
tN = 0.0;
// recompute sc for this edge
if (-d < 0.0)
{
sN = 0.0;
}
else if (-d > a)
{
sN = sD;
}
else
{
sN = -d;
sD = a;
}
}
else if (tN > tD)
{
// tc > 1 => the t = 1 edge is visible
// recompute sc for this edge
if ((-d + b) < 0.0)
{
sN = 0;
}
else if ((-d + b) > a)
{
sN = sD;
}
else
{
sN = (-d + b);
sD = a;
}
}
// finally do the division to get sc and tc
if (Math.Abs(sN) < smallNum)
{
sc = 0.0;
}
else
{
sc = sN / sD;
}
if (Math.Abs(tN) < smallNum)
{
tc = 0.0;
}
else
{
tc = tN / tD;
}
// get the difference of the two closest points
Vector dU = u.Multiply(sc);
Vector dV = v.Multiply(tc);
Vector dP = (w.Add(dU)).Subtract(dV);
// S1(sc) - S2(tc)
return dP.Length2D;
}
/// <summary>
/// Returns 0 if no intersections occur, 1 if an intersection point is found,
/// and 2 if the segments are colinear and overlap.
/// </summary>
/// <param name="other"></param>
/// <returns></returns>
public int IntersectionCount(Segment other)
{
double x1 = P1.X;
double y1 = P1.Y;
double x2 = P2.X;
double y2 = P2.Y;
double x3 = other.P1.X;
double y3 = other.P1.Y;
double x4 = other.P2.X;
double y4 = other.P2.Y;
double denom = (y4 - y3) * (x2 - x1) - (x4 - x3) * (y2 - y1);
//The case of two degenerate segements
if ((x1 == x2) && (y1 == y2) && (x3 == x4) && (y3 == y4))
{
if ((x1 != x3) || (y1 != y3))
return 0;
}
// if denom is 0, then the two lines are parallel
double na = (x4 - x3) * (y1 - y3) - (y4 - y3) * (x1 - x3);
double nb = (x2 - x1) * (y1 - y3) - (y2 - y1) * (x1 - x3);
// if denom is 0 AND na and nb are 0, then the lines are coincident and DO intersect
if (Math.Abs(denom) < Epsilon && Math.Abs(na) < Epsilon && Math.Abs(nb) < Epsilon) return 2;
// If denom is 0, but na or nb are not 0, then the lines are parallel and not coincident
if (denom == 0) return 0;
double ua = na / denom;
double ub = nb / denom;
if (ua < 0 || ua > 1) return 0; // not intersecting with segment a
if (ub < 0 || ub > 1) return 0; // not intersecting with segment b
// If we get here, then one intersection exists and it is found on both line segments
return 1;
}
/// <summary>
/// For each coordinate in the other part, if it falls in the extent of this polygon, a
/// ray crossing test is used for point in polygon testing. If it is not in the extent,
/// it is skipped.
/// </summary>
/// <param name="polygonShape">The part of the polygon to analyze polygon</param>
/// <param name="otherPart">The other part</param>
/// <returns>Boolean, true if any coordinate falls inside the polygon</returns>
private static bool ContainsVertex(ShapeRange polygonShape, PartRange otherPart)
{
// Create an extent for faster checking in most cases
Extent ext = polygonShape.Extent;
foreach (Vertex point in otherPart)
{
// This extent check shortcut should help speed things up for large polygon parts
if (!ext.Intersects(point)) continue;
// Imagine a ray on the horizontal starting from point.X -> infinity. (In practice this can be ext.XMax)
// Count the intersections of segments with that line. If the resulting count is odd, the point is inside.
Segment ray = new Segment(point.X, point.Y, ext.MaxX, point.Y);
int[] numCrosses = new int[polygonShape.NumParts]; // A cross is a complete cross. Coincident doesn't count because it is either 0 or 2 crosses.
int totalCrosses = 0;
int iPart = 0;
foreach (PartRange ring in polygonShape.Parts)
{
foreach (Segment segment in ring.Segments)
{
if (segment.IntersectionCount(ray) != 1) continue;
numCrosses[iPart]++;
totalCrosses++;
}
iPart++;
}
// If we didn't actually have any polygons we cant intersect with anything
if (polygonShape.NumParts < 1) return false;
// For shapes with only one part, we don't need to test part-containment.
if (polygonShape.NumParts == 1 && totalCrosses % 2 == 1) return true;
// This used to check to see if totalCrosses == 1, but now checks to see if totalCrosses is an odd number.
// This change was made to solve the issue described in HD Issue 8593 (http://hydrodesktop.codeplex.com/workitem/8593).
if (totalCrosses % 2 == 1) return true;
totalCrosses = 0;
for (iPart = 0; iPart < numCrosses.Length; iPart++)
{
int count = numCrosses[iPart];
// If this part does not contain the point, don't bother trying to figure out if the part is a hole or not.
if (count % 2 == 0) continue;
// If this particular part is a hole, subtract the total crosses by 1, otherwise add one.
// This takes time, so we want to do this as few times as possible.
if (polygonShape.Parts[iPart].IsHole())
{
totalCrosses--;
}
else
{
totalCrosses++;
}
}
return totalCrosses > 0;
}
return false;
}
