--- a/pkg/octree/vertex.go	Wed Jun 12 17:30:20 2019 +0200
+++ b/pkg/octree/vertex.go	Thu Jun 13 13:14:40 2019 +0200
@@ -210,6 +210,11 @@
 	return math.Hypot(v.X-w.X, v.Y-w.Y)
 }
 
+func (v Vertex) Distance(w Vertex) float64 {
+	v = v.Sub(w)
+	return math.Sqrt(v.Dot(v))
+}
+
 // Minimize adjust this vertex v to hold the minimum
 // values component-wise of v and w.
 func (v *Vertex) Minimize(w Vertex) {
@@ -441,6 +446,34 @@
 	}
 }
 
+func (ls LineStringZ) Buffer(radius float64) {
+	if len(ls) == 0 {
+		return
+	}
+	var cx, cy, cz float64
+	for i := range ls {
+		cx += ls[i].X
+		cy += ls[i].Y
+		cz += ls[i].Z
+	}
+
+	s := 1.0 / float64(len(ls))
+
+	cx *= s
+	cy *= s
+	cz *= s
+	c := Vertex{X: cx, Y: cy, Z: cz}
+	for i := range ls {
+		n := c.Sub(ls[i]).Normalize()
+		l := ls[i].Distance(c)
+		// l = 1
+		// l + r = s
+		// (l+r)/l = s
+		s := (l + radius) / l
+		ls[i] = ls[i].Add(n.Scale(s))
+	}
+}
+
 func (ls LineStringZ) order(position func(Vertex) float64) {
 	type posVertex struct {
 		pos float64