public static XYZ TransformPoint(XYZ point, Transform transform)
{
    double x = point.X;
    double y = point.Y;
    double z = point.Z;

    //transform basis of the old coordinate system in the new coordinate // system
    XYZ b0 = transform.get_Basis(0);
    XYZ b1 = transform.get_Basis(1);
    XYZ b2 = transform.get_Basis(2);
    XYZ origin = transform.Origin;

    //transform the origin of the old coordinate system in the new 
    //coordinate system
    double xTemp = x * b0.X + y * b1.X + z * b2.X + origin.X;
    double yTemp = x * b0.Y + y * b1.Y + z * b2.Y + origin.Y;
    double zTemp = x * b0.Z + y * b1.Z + z * b2.Z + origin.Z;

    return new XYZ(xTemp, yTemp, zTemp);
}

Public Shared Function TransformPoint(point As XYZ, transform As Transform) As XYZ
    Dim x As Double = point.X
    Dim y As Double = point.Y
    Dim z As Double = point.Z

    'transform basis of the old coordinate system in the new coordinate // system
    Dim b0 As XYZ = transform.Basis(0)
    Dim b1 As XYZ = transform.Basis(1)
    Dim b2 As XYZ = transform.Basis(2)
    Dim origin As XYZ = transform.Origin

    'transform the origin of the old coordinate system in the new 
    'coordinate system
    Dim xTemp As Double = x * b0.X + y * b1.X + z * b2.X + origin.X
    Dim yTemp As Double = x * b0.Y + y * b1.Y + z * b2.Y + origin.Y
    Dim zTemp As Double = x * b0.Z + y * b1.Z + z * b2.Z + origin.Z

    Return New XYZ(xTemp, yTemp, zTemp)
End Function