//--------------------------------------------------------------------------------------------------
public gp_Sphere GetOrbitSphere()
{
double xEye = 0, yEye = 0, zEye = 0, xAt = 0, yAt = 0, zAt = 0;
V3dView.Eye(ref xEye, ref yEye, ref zEye);
V3dView.At(ref xAt, ref yAt, ref zAt);
Pnt eyePoint = new Pnt(xEye, yEye, zEye);
Pnt atPoint = new Pnt(xAt, yAt, zAt);
var eyeVector = new Vec(eyePoint, atPoint);
return(new gp_Sphere(new Ax3(atPoint, Dir.DZ, -Dir.DY.Rotated(Ax1.OZ, V3dView.Twist())), eyeVector.Magnitude()));
}