public void testIntersectionTolerance()
{
// We repeatedly construct two edges that cross near a random point "p",
// and measure the distance from the actual intersection point "x" to the
// the expected intersection point "p" and also to the edges that cross
// near "p".
//
// Note that getIntersection() does not guarantee that "x" and "p" will be
// close together (since the intersection point is numerically unstable
// when the edges cross at a very small angle), but it does guarantee that
// "x" will be close to both of the edges that cross.
var maxPointDist = new S1Angle();
var maxEdgeDist = new S1Angle();
for (var i = 0; i < 1000; ++i)
{
// We construct two edges AB and CD that intersect near "p". The angle
// between AB and CD (expressed as a slope) is chosen randomly between
// 1e-15 and 1.0 such that its logarithm is uniformly distributed. This
// implies that small values are much more likely to be chosen.
//
// Once the slope is chosen, the four points ABCD must be offset from P
// by at least (1e-15 / slope) so that the points are guaranteed to have
// the correct circular ordering around P. This is the distance from P
// at which the two edges are separated by about 1e-15, which is
// approximately the minimum distance at which we can expect computed
// points on the two lines to be distinct and have the correct ordering.
//
// The actual offset distance from P is chosen randomly in the range
// [1e-15 / slope, 1.0], again uniformly distributing the logarithm.
// This ensures that we test both long and very short segments that
// intersect at both large and very small angles.
var points = getRandomFrame();
var p = points[0];
var d1 = points[1];
var d2 = points[2];
var slope = Math.Pow(1e-15, rand.NextDouble());
d2 = d1 + (d2 * slope);
var a = S2Point.Normalize(p + (d1 * Math.Pow(1e-15 / slope, rand.NextDouble())));
var b = S2Point.Normalize(p - (d1 * Math.Pow(1e-15 / slope, rand.NextDouble())));
var c = S2Point.Normalize(p + (d2 * Math.Pow(1e-15 / slope, rand.NextDouble())));
var d = S2Point.Normalize(p - (d2 * Math.Pow(1e-15 / slope, rand.NextDouble())));
var x = S2EdgeUtil.GetIntersection(a, b, c, d);
var distAb = S2EdgeUtil.GetDistance(x, a, b);
var distCd = S2EdgeUtil.GetDistance(x, c, d);
assertTrue(distAb < S2EdgeUtil.DefaultIntersectionTolerance);
assertTrue(distCd < S2EdgeUtil.DefaultIntersectionTolerance);
// test getIntersection() post conditions
assertTrue(S2.OrderedCcw(a, x, b, S2Point.Normalize(S2.RobustCrossProd(a, b))));
assertTrue(S2.OrderedCcw(c, x, d, S2Point.Normalize(S2.RobustCrossProd(c, d))));
maxEdgeDist = S1Angle.Max(maxEdgeDist, S1Angle.Max(distAb, distCd));
maxPointDist = S1Angle.Max(maxPointDist, new S1Angle(p, x));
}
}
private void dumpCrossings(S2Loop loop)
{
Console.WriteLine("Ortho(v1): " + S2.Ortho(loop.Vertex(1)));
Console.WriteLine("Contains(kOrigin): {0}\n", loop.Contains(S2.Origin));
for (var i = 1; i <= loop.NumVertices; ++i)
{
var a = S2.Ortho(loop.Vertex(i));
var b = loop.Vertex(i - 1);
var c = loop.Vertex(i + 1);
var o = loop.Vertex(i);
Console.WriteLine("Vertex {0}: [%.17g, %.17g, %.17g], "
+ "%d%dR=%d, %d%d%d=%d, R%d%d=%d, inside: %b\n",
i,
loop.Vertex(i).X,
loop.Vertex(i).Y,
loop.Vertex(i).Z,
i - 1,
i,
S2.RobustCcw(b, o, a),
i + 1,
i,
i - 1,
S2.RobustCcw(c, o, b),
i,
i + 1,
S2.RobustCcw(a, o, c),
S2.OrderedCcw(a, b, c, o));
}
for (var i = 0; i < loop.NumVertices + 2; ++i)
{
var orig = S2.Origin;
S2Point dest;
if (i < loop.NumVertices)
{
dest = loop.Vertex(i);
Console.WriteLine("Origin->{0} crosses:", i);
}
else
{
dest = new S2Point(0, 0, 1);
if (i == loop.NumVertices + 1)
{
orig = loop.Vertex(1);
}
Console.WriteLine("Case {0}:", i);
}
for (var j = 0; j < loop.NumVertices; ++j)
{
Console.WriteLine(
" " + S2EdgeUtil.EdgeOrVertexCrossing(orig, dest, loop.Vertex(j), loop.Vertex(j + 1)));
}
Console.WriteLine();
}
for (var i = 0; i <= 2; i += 2)
{
Console.WriteLine("Origin->v1 crossing v{0}->v1: ", i);
var a = S2.Ortho(loop.Vertex(1));
var b = loop.Vertex(i);
var c = S2.Origin;
var o = loop.Vertex(1);
Console.WriteLine("{0}1R={1}, M1{2}={3}, R1M={4}, crosses: {5}\n",
i,
S2.RobustCcw(b, o, a),
i,
S2.RobustCcw(c, o, b),
S2.RobustCcw(a, o, c),
S2EdgeUtil.EdgeOrVertexCrossing(c, o, b, a));
}
}
