private static double[][] GetTessTrianglesTs(this IFace2 face, bool noConversion) { var data = (double[])face.GetTessTriangles(noConversion); return(data.Select((value, index) => new { value, index }) .GroupBy(x => x.index / 3, x => x.value) // a group is a point of the triangle .Select(x => x.ToArray()) .ToArray()); }