--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/cmd/octree2contour/vertex.go	Wed Sep 19 13:26:30 2018 +0200
@@ -0,0 +1,54 @@
+package main
+
+type vertex struct {
+	x float64
+	y float64
+	z float64
+}
+
+func (v *vertex) minimize(w vertex) {
+	if w.x < v.x {
+		v.x = w.x
+	}
+	if w.y < v.y {
+		v.y = w.y
+	}
+	if w.z < v.z {
+		v.z = w.z
+	}
+}
+
+func (v *vertex) maximize(w vertex) {
+	if w.x > v.x {
+		v.x = w.x
+	}
+	if w.y > v.y {
+		v.y = w.y
+	}
+	if w.z > v.z {
+		v.z = w.z
+	}
+}
+
+func (v vertex) sub(w vertex) vertex {
+	return vertex{
+		v.x - w.x,
+		v.y - w.y,
+		v.z - w.z,
+	}
+}
+
+func interpolate(v1, v2 vertex) func(vertex) vertex {
+	v2 = v2.sub(v1)
+	return func(s vertex) vertex {
+		return vertex{
+			v2.x*s.x + v1.x,
+			v2.y*s.y + v1.y,
+			v2.z*s.z + v1.z,
+		}
+	}
+}
+
+func (a vertex) less(b vertex) bool {
+	return a.x < b.x || a.y < b.y || a.z < b.z
+}