C++ Point2D::norm2方法代码示例

float Classifier::classify2D_checkcondnum(const Point2D& P, const Point2D& R, float& condnumber) const
{
	condnumber = 0;
	if (path.size() < 2)
	{
		assert(false);
		return 0;
	}

	// consider each path segment as a mini-classifier
	// the segment PR[Pt-->Refpt] and each path's segment cross
	// iff each one classifies the end point of the other in different classes
	Point2D PR = R-P;
	Point2D u = PR; u.normalize();

	unsigned numcross = 0;

	//we'll also look for the distance between P and the nearest segment
	float closestSquareDist = -1.0f;

	size_t segCount = path.size() - 1;
	for (size_t i=0; i<segCount; ++i)
	{
		//current path segment (or half-line!)
		Point2D AP = P - path[i];
		Point2D AB = path[i+1] - path[i];
		Point2D v = AB; v.normalize();

		condnumber = std::max<float>(condnumber, fabs(v.dot(u)));

		// Compute whether PR[Pt-->Refpt] and that segment cross
		float denom = (u.x*v.y-v.x*u.y);
		if (denom != 0)
		{
			// 1. check whether the given pt and the refpt are on different sides of the classifier line
			//we search for alpha and beta so that
			// P + alpha * PR = A + beta * AB
			float alpha = (AP.y * v.x - AP.x * v.y)/denom;
			bool pathIntersects = (alpha >= 0 && alpha*alpha <= PR.norm2());
			if (pathIntersects)
			{
				float beta = (AP.y * u.x - AP.x * u.y)/denom;

				// first and last lines are projected to infinity
				bool refSegIntersects = ((i == 0 || beta >= 0) && (i+1 == segCount || beta*beta < AB.norm2())); //not "beta*beta <= AB.norm2()" because the equality case will be managed by the next segment!

				// crossing iif each segment/line separates the other
				if (refSegIntersects)
					numcross++;
			}
		}

		// closest distance from the point to that segment
		// 1. projection of the point of the line
		float squareDistToSeg = 0;
		float distAH = v.dot(AP);
		if ((i == 0 || distAH >= 0.0) && (i+1 == segCount || distAH <= AB.norm()))
		{
			// 2. Is the projection within the segment limit? yes => closest
			Point2D PH = (path[i] + v * distAH) - P;
			squareDistToSeg = PH.norm2();
		}
		else
		{
			// 3. otherwise closest is the minimum of the distance to the segment ends
			Point2D BP = P - path[i+1];
			squareDistToSeg = std::min( AP.norm2(), BP.norm2() );
		}

		if (closestSquareDist < 0 || squareDistToSeg < closestSquareDist)
		{
			closestSquareDist = squareDistToSeg;
		}
	}

	assert(closestSquareDist >= 0);
	float deltaNorm = sqrt(closestSquareDist);

	return ((numcross & 1) == 0 ? deltaNorm : -deltaNorm);
}