public void Test_GetLengthAndCentroid_GreatCircles()
{
// Construct random great circles and divide them randomly into segments.
// Then make sure that the length and centroid are correct. Note that
// because of the way the centroid is computed, it does not matter how
// we split the great circle into segments.
for (int iter = 0; iter < 100; ++iter)
{
// Choose a coordinate frame for the great circle.
S2Testing.GetRandomFrame(out var x, out var y, out _);
var lineList = new List <S2Point>();
double theta = 0;
while (theta < S2.M_2_PI)
{
lineList.Add(Math.Cos(theta) * x + Math.Sin(theta) * y);
theta += S2Testing.Random.RandDouble();
}
// Close the circle.
lineList.Add(lineList[0]);
var line = lineList.ToArray();
S1Angle length = S2PolylineMeasures.GetLength(line);
Assert.True(Math.Abs(length.Radians - S2.M_2_PI) <= 2e-14);
S2Point centroid = S2PolylineMeasures.GetCentroid(line);
Assert.True(centroid.Norm() <= 2e-14);
}
}
// For shapes of dimension 1, returns the sum of all polyline lengths on the
// unit sphere. Otherwise returns zero. (See GetPerimeter for shapes of
// dimension 2.)
//
// All edges are modeled as spherical geodesics. The result can be converted
// to a distance on the Earth's surface (with a worst-case error of 0.562%
// near the equator) using the functions in s2earth.h.
public static S1Angle GetLength(S2Shape shape)
{
if (shape.Dimension() != 1)
{
return(S1Angle.Zero);
}
var length = S1Angle.Zero;
int num_chains = shape.NumChains();
for (int chain_id = 0; chain_id < num_chains; ++chain_id)
{
GetChainVertices(shape, chain_id, out var vertices);
length += S2PolylineMeasures.GetLength(vertices);
}
return(length);
}