Sets the start parameter for the elliptical figure (ellipse or arc) (DXF 41). Parameter is an angle measured from the major axis in the range 0 to 2PI radians as if the elliptical figure was a circular figure with a major radius. A positive value specifies the start parameter measured counterclockwise A negative value specifies the start parameter measured clockwise. The initial value is zero by default. 

If an parameter 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 (StartParam = 0) and (EndParam = Oda2PI) or |EndParam - StartParam| <= 1e-7, the figure is closed, that is an ellipse.

Example of Working with the Ellipse Object 

Example of Working with the Elliptical Arc 

Computed Ellipse and Elliptical Arc Properties 

Specific Elliptical Arc Properties 

OdDbEllipse::getStartParam() method 

OdDbEllipse::setEndParam() method