///<summary>
/// Counts a segment
///</summary>
/// <param name="p1">An endpoint of the segment</param>
/// <param name="p2">Another endpoint of the segment</param>
public void CountSegment(Coordinate p1, Coordinate p2)
{
/*
* For each segment, check if it crosses
* a horizontal ray running from the test point in the positive x direction.
*/
// check if the segment is strictly to the left of the test point
if (p1.X < _p.X && p2.X < _p.X)
{
return;
}
// check if the point is equal to the current ring vertex
if (_p.X == p2.X && _p.Y == p2.Y)
{
_isPointOnSegment = true;
return;
}
/*
* For horizontal segments, check if the point is on the segment.
* Otherwise, horizontal segments are not counted.
*/
if (p1.Y == _p.Y && p2.Y == _p.Y)
{
double minx = p1.X;
double maxx = p2.X;
if (minx > maxx)
{
minx = p2.X;
maxx = p1.X;
}
if (_p.X >= minx && _p.X <= maxx)
{
_isPointOnSegment = true;
}
return;
}
/*
* Evaluate all non-horizontal segments which cross a horizontal ray to the
* right of the test pt. To avoid double-counting shared vertices, we use the
* convention that
* <ul>
* <li>an upward edge includes its starting endpoint, and excludes its
* final endpoint
* <li>a downward edge excludes its starting endpoint, and includes its
* final endpoint
* </ul>
*/
if (((p1.Y > _p.Y) && (p2.Y <= _p.Y)) ||
((p2.Y > _p.Y) && (p1.Y <= _p.Y)))
{
// translate the segment so that the test point lies on the origin
double x1 = p1.X - _p.X;
double y1 = p1.Y - _p.Y;
double x2 = p2.X - _p.X;
double y2 = p2.Y - _p.Y;
/*
* The translated segment straddles the x-axis. Compute the sign of the
* ordinate of intersection with the x-axis. (y2 != y1, so denominator
* will never be 0.0)
*/
// double xIntSign = RobustDeterminant.signOfDet2x2(x1, y1, x2, y2) / (y2
// - y1);
// MD - faster & more robust computation?
double xIntSign = RobustDeterminant.SignOfDet2x2(x1, y1, x2, y2);
if (xIntSign == 0.0)
{
_isPointOnSegment = true;
return;
}
if (y2 < y1)
{
xIntSign = -xIntSign;
}
// xsave = xInt;
// The segment crosses the ray if the sign is strictly positive.
if (xIntSign > 0.0)
{
_crossingCount++;
}
}
}
