Title: How to Determine the vertex angle made by two 3D segments
function VertexAngle(x1, y1, z1, x2, y2, z2, x3, y3, z3: Double): Double;
var
Dist: Double;
begin
(* Quantify coordinates *)
x1 := x1 - x2;
x3 := x3 - x2;
y1 := y1 - y2;
y3 := y3 - y2;
z1 := z1 - z2;
z3 := z3 - z2;
(* Calculate Lay Distance *)
Dist := (x1 * x1 + y1 * y1 + z1 * z1) * (x3 * x3 + y3 * y3 + z3 * z3);
if IsEqual(Dist, 0) then Result := 0.0
else
Result := ArcCos((x1 * x3 + y1 * y3 + z1 * z3) / sqrt(Dist)) * _180DivPI;
end;
(* End Of VertexAngle *)