/// <summary>
/// Calculate the area enclosed by this curve, were the start and end points to be
/// joined by a straight line segment.
/// A plane may optionally be specified, otherwise by default the projected area on
/// the XY plane will be used.
/// </summary>
/// <param name="centroid">Output. The centroid of the enclosed area, in local coordinates
/// on the specified plane.</param>
/// <param name="onPlane">The plane to use to calculate the area.
/// If not specified, the XY plane will be used.</param>
/// <returns>The signed area enclosed by this curve on the specified plane,
/// as a double.</returns>
public override double CalculateEnclosedArea(out Vector centroid, Plane onPlane = null)
{
double result = 0;
centroid = Vector.Zero;
for (int i = 0; i < SubCurves.Count; i++)
{
Curve subCrv = SubCurves[i];
Vector start = subCrv.StartPoint;
Vector end = subCrv.EndPoint;
if (onPlane != null)
{
start = onPlane.GlobalToLocal(start);
end = onPlane.GlobalToLocal(end);
}
double areaUnder = MathsHelper.AreaUnder(start.X, start.Y, end.X, end.Y, ref centroid);
result += areaUnder;
Vector subCentroid;
double subArea = subCrv.CalculateEnclosedArea(out subCentroid, onPlane);
result += subArea;
centroid += subCentroid * subArea;
}
centroid /= result;
return(result);
}