ArcGIS Pro 2.6 API Reference Guide
Orientation Property (EllipticArcBuilder)
Example 

ArcGIS.Core.Geometry Namespace > EllipticArcBuilder Class : Orientation Property
Gets the orientation of this elliptical arc. This method must be called on the MCT. Use QueuedTask.Run.
Syntax
public esriArcOrientation Orientation {get;}
Public ReadOnly Property Orientation As esriArcOrientation
Exceptions
ExceptionDescription
This method or property must be called within the lambda passed to QueuedTask.Run.
Example
// Builder constructors need to run on the MCT.
ArcGIS.Desktop.Framework.Threading.Tasks.QueuedTask.Run(() =>
{
  // retrieve the curve's control points
  using (EllipticArcBuilder builder = new EllipticArcBuilder(arcSegment))
  {
    MapPoint startPt = builder.StartPoint;
    MapPoint endPt = builder.EndPoint;
    Coordinate2D centerPt = builder.CenterPoint;
    bool isCircular = builder.IsCircular;
    bool isMinor = builder.IsMinor;
    double startAngle = builder.StartAngle;
    double endAngle = builder.EndAngle;
    double centralAngle = builder.CentralAngle;
    double rotationAngle = builder.RotationAngle;
    esriArcOrientation orientation = builder.Orientation;
  }
});
Requirements

Target Platforms: Windows 10, Windows 8.1, Windows 7

See Also

Reference

EllipticArcBuilder Class
EllipticArcBuilder Members