public double StartDirection {get; set;}

GeodesicSectorParameter param = new GeodesicSectorParameter();
param.ArcVertexCount = 50;
param.AxisDirection = Math.PI / 4;
param.Center = new Coordinate2D(0, 0);
param.LinearUnit = LinearUnit.Meters;
param.OutGeometryType = GeometryType.Polygon;
param.RadiusVertexCount = 10;
param.SectorAngle = 5 * Math.PI / 3;
param.SemiAxis1Length = 100000;
param.SemiAxis2Length = 20000;
param.StartDirection = 11 * Math.PI / 6;

Geometry geometry = GeometryEngine.Instance.GeodesicSector(param, SpatialReferences.WGS84);
// geometry.IsEmpty = false

Polygon polygon = geometry as Polygon;
// polygon.PointCount = 68
// polygon.PartCount = 1