public List <SimpleSurface> DecomposeToSimpleSurfaces()
{
var topSeg = _top.Decompose();
var botSeg = _bottom.Decompose();
return(topSeg
.Select((t, i) => new SimpleSurface(new List <Point3>
{
t.P1,
t.P2,
botSeg[i].P2,
botSeg[i].P1
})).ToList());
}