private Vector3d CreateSunVector()
{
/* set up a horizontal curve in the y direction that can be rotated */
Point3d myStartPoint = new Point3d(0.0, 0.0, 0.0);
Point3d myEndPoint = new Point3d(0.0, -100.0, 0.0);
LineCurve myCurve = new LineCurve();
myCurve.SetStartPoint(myStartPoint);
myCurve.SetEndPoint(myEndPoint);
/* set up axis of rotation for both altitude and azumith angles */
Vector3d altitudeAxis = new Vector3d(1.0, 0.0, 0.0);
Vector3d azumithAxis = new Vector3d(0.0, 0.0, 1.0);
/* rotate by curve */
myCurve.Rotate(altitudeAngle, altitudeAxis, myStartPoint);
myCurve.Rotate(azumithAngle, azumithAxis, myStartPoint);
/* set up the line from the start and end points of the curve so that the direction vector can be derived */
Line vectorLine = new Line(myCurve.PointAtStart, myCurve.PointAtEnd);
Vector3d mySunVector = new Vector3d(vectorLine.Direction);
return(mySunVector);
}