public void Test_S2Cap_Basic()
{
// Test basic properties of empty and full caps.
S2Cap empty = S2Cap.Empty;
S2Cap full = S2Cap.Full;
Assert.True(empty.IsValid());
Assert.True(empty.IsEmpty());
Assert.True(empty.Complement().IsFull());
Assert.True(full.IsValid());
Assert.True(full.IsFull());
Assert.True(full.Complement().IsEmpty());
Assert.Equal(2, full.Height());
Assert2.DoubleEqual(180.0, full.Radius.Degrees());
// Test ==/!=.
Assert.Equal(full, full);
Assert.Equal(empty, empty);
Assert.NotEqual(full, empty);
// Test the S1Angle constructor using out-of-range arguments.
Assert.True(new S2Cap(new S2Point(1, 0, 0), S1Angle.FromRadians(-20)).IsEmpty());
Assert.True(new S2Cap(new S2Point(1, 0, 0), S1Angle.FromRadians(5)).IsFull());
Assert.True(new S2Cap(new S2Point(1, 0, 0), S1Angle.Infinity).IsFull());
// Check that the default S2Cap is identical to Empty().
var default_empty = S2Cap.Empty;
Assert.True(default_empty.IsValid());
Assert.True(default_empty.IsEmpty());
Assert.Equal(empty.Center, default_empty.Center);
Assert.Equal(empty.Height(), default_empty.Height());
// Containment and intersection of empty and full caps.
Assert.True(empty.Contains(empty));
Assert.True(full.Contains(empty));
Assert.True(full.Contains(full));
Assert.False(empty.InteriorIntersects(empty));
Assert.True(full.InteriorIntersects(full));
Assert.False(full.InteriorIntersects(empty));
// Singleton cap containing the x-axis.
S2Cap xaxis = S2Cap.FromPoint(new S2Point(1, 0, 0));
Assert.True(xaxis.Contains(new S2Point(1, 0, 0)));
Assert.False(xaxis.Contains(new S2Point(1, 1e-20, 0)));
Assert.Equal(0, xaxis.Radius.Radians());
// Singleton cap containing the y-axis.
S2Cap yaxis = S2Cap.FromPoint(new S2Point(0, 1, 0));
Assert.False(yaxis.Contains(xaxis.Center));
Assert.Equal(0, xaxis.Height());
// Check that the complement of a singleton cap is the full cap.
S2Cap xcomp = xaxis.Complement();
Assert.True(xcomp.IsValid());
Assert.True(xcomp.IsFull());
Assert.True(xcomp.Contains(xaxis.Center));
// Check that the complement of the complement is *not* the original.
Assert.True(xcomp.Complement().IsValid());
Assert.True(xcomp.Complement().IsEmpty());
Assert.False(xcomp.Complement().Contains(xaxis.Center));
// Check that very small caps can be represented accurately.
// Here "kTinyRad" is small enough that unit vectors perturbed by this
// amount along a tangent do not need to be renormalized.
S2Cap tiny = new(new S2Point(1, 2, 3).Normalize(), S1Angle.FromRadians(kTinyRad));
var tangent = tiny.Center.CrossProd(new S2Point(3, 2, 1)).Normalize();
Assert.True(tiny.Contains(tiny.Center + 0.99 * kTinyRad * tangent));
Assert.False(tiny.Contains(tiny.Center + 1.01 * kTinyRad * tangent));
// Basic tests on a hemispherical cap.
S2Cap hemi = S2Cap.FromCenterHeight(new S2Point(1, 0, 1).Normalize(), 1);
Assert.Equal(-hemi.Center, hemi.Complement().Center);
Assert.Equal(1, hemi.Complement().Height());
Assert.True(hemi.Contains(new S2Point(1, 0, 0)));
Assert.False(hemi.Complement().Contains(new S2Point(1, 0, 0)));
Assert.True(hemi.Contains(new S2Point(1, 0, -(1 - kEps)).Normalize()));
Assert.False(hemi.InteriorContains(new S2Point(1, 0, -(1 + kEps)).Normalize()));
// A concave cap. Note that the error bounds for point containment tests
// increase with the cap angle, so we need to use a larger error bound
// here. (It would be painful to do this everywhere, but this at least
// gives an example of how to compute the maximum error.)
S2Point center = GetLatLngPoint(80, 10);
S1ChordAngle radius = new(S1Angle.FromDegrees(150));
double max_error =
radius.GetS2PointConstructorMaxError() +
radius.S1AngleConstructorMaxError +
3 * S2.DoubleEpsilon; // GetLatLngPoint() error
S2Cap concave = new(center, radius);
S2Cap concave_min = new(center, radius.PlusError(-max_error));
S2Cap concave_max = new(center, radius.PlusError(max_error));
Assert.True(concave_max.Contains(GetLatLngPoint(-70, 10)));
Assert.False(concave_min.Contains(GetLatLngPoint(-70, 10)));
Assert.True(concave_max.Contains(GetLatLngPoint(-50, -170)));
Assert.False(concave_min.Contains(GetLatLngPoint(-50, -170)));
// Cap containment tests.
Assert.False(empty.Contains(xaxis));
Assert.False(empty.InteriorIntersects(xaxis));
Assert.True(full.Contains(xaxis));
Assert.True(full.InteriorIntersects(xaxis));
Assert.False(xaxis.Contains(full));
Assert.False(xaxis.InteriorIntersects(full));
Assert.True(xaxis.Contains(xaxis));
Assert.False(xaxis.InteriorIntersects(xaxis));
Assert.True(xaxis.Contains(empty));
Assert.False(xaxis.InteriorIntersects(empty));
Assert.True(hemi.Contains(tiny));
Assert.True(hemi.Contains(new S2Cap(new S2Point(1, 0, 0), S1Angle.FromRadians(S2.M_PI_4 - kEps))));
Assert.False(hemi.Contains(new S2Cap(new S2Point(1, 0, 0), S1Angle.FromRadians(S2.M_PI_4 + kEps))));
Assert.True(concave.Contains(hemi));
Assert.True(concave.InteriorIntersects(hemi.Complement()));
Assert.False(concave.Contains(S2Cap.FromCenterHeight(-concave.Center, 0.1)));
}