Sets the start angle for the elliptical figure (ellipse or arc) in the range ±2PI radians (DXF 50). A positive value specifies the angle measured from the major axis counterclockwise. A negative value specifies the angle measured from the major axis clockwise. The initial value is zero by default. 

If an angle value is negative, this method automatically converts it to the positive equivalent. If an angle value is more than 2PI, this method automatically convertes it to the range 0 to 2PI. When (StartAngle = 0) and (EndAngle = Oda2PI) or |EndAngle - StartAngle| <= 1e-12, the figure is closed, that is an ellipse.

Example of Working with the Elliptical Arc 

Specific Elliptical Arc Properties 

OdDbEllipse::startAngle() method 

OdDbEllipse::setEndAngle() method