--- a/cmd/octree2contour/vertex.go	Sat Sep 22 09:55:42 2018 +0200
+++ b/cmd/octree2contour/vertex.go	Sat Sep 22 21:34:12 2018 +0200
@@ -1,12 +1,27 @@
 package main
 
-type vertex struct {
-	x float64
-	y float64
-	z float64
-}
+import (
+	"encoding/binary"
+	"io"
+	"math"
+)
 
-func (v *vertex) minimize(w vertex) {
+type (
+	Vertex struct {
+		x float64
+		y float64
+		z float64
+	}
+
+	Triangle [3]Vertex
+
+	Line [2]Vertex
+
+	LineStringZ      []Vertex
+	MultiLineStringZ []LineStringZ
+)
+
+func (v *Vertex) Minimize(w Vertex) {
 	if w.x < v.x {
 		v.x = w.x
 	}
@@ -18,7 +33,7 @@
 	}
 }
 
-func (v *vertex) maximize(w vertex) {
+func (v *Vertex) Maximize(w Vertex) {
 	if w.x > v.x {
 		v.x = w.x
 	}
@@ -30,34 +45,34 @@
 	}
 }
 
-func (v vertex) sub(w vertex) vertex {
-	return vertex{
+func (v Vertex) Sub(w Vertex) Vertex {
+	return Vertex{
 		v.x - w.x,
 		v.y - w.y,
 		v.z - w.z,
 	}
 }
 
-func (v vertex) add(w vertex) vertex {
-	return vertex{
+func (v Vertex) Add(w Vertex) Vertex {
+	return Vertex{
 		v.x + w.x,
 		v.y + w.y,
 		v.z + w.z,
 	}
 }
 
-func (v vertex) scale(s float64) vertex {
-	return vertex{
+func (v Vertex) scale(s float64) Vertex {
+	return Vertex{
 		s * v.x,
 		s * v.y,
 		s * v.z,
 	}
 }
 
-func interpolate(v1, v2 vertex) func(vertex) vertex {
-	v2 = v2.sub(v1)
-	return func(s vertex) vertex {
-		return vertex{
+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,
@@ -65,30 +80,26 @@
 	}
 }
 
-func (a vertex) less(b vertex) bool {
+func (a Vertex) Less(b Vertex) bool {
 	return a.x < b.x || a.y < b.y || a.z < b.z
 }
 
-type line [2]vertex
-
-func newLine(p1, p2 vertex) line {
-	return line{
-		p2.sub(p1),
+func NewLine(p1, p2 Vertex) Line {
+	return Line{
+		p2.Sub(p1),
 		p1,
 	}
 }
 
-func (l line) eval(t float64) vertex {
-	return l[0].scale(t).add(l[1])
+func (l Line) Eval(t float64) Vertex {
+	return l[0].scale(t).Add(l[1])
 }
 
-func (l line) intersectH(h float64) vertex {
+func (l Line) IntersectHorizontal(h float64) Vertex {
 	t := (h - l[1].z) / l[0].z
-	return l.eval(t)
+	return l.Eval(t)
 }
 
-type triangle [3]vertex
-
 func side(z, h float64) int {
 	switch {
 	case z < h:
@@ -99,14 +110,14 @@
 	return 0
 }
 
-func (t *triangle) intersectH(h float64) lineStringZ {
+func (t *Triangle) IntersectHorizontal(h float64) LineStringZ {
 	sides := [3]int{
 		side(t[0].z, h),
 		side(t[1].z, h),
 		side(t[2].z, h),
 	}
 
-	var points lineStringZ
+	var points LineStringZ
 
 	for i := 0; i < 3; i++ {
 		j := (i + 1) % 3
@@ -127,10 +138,28 @@
 			// both on same side
 		default:
 			// real intersection
-			v := newLine(t[i], t[j]).intersectH(h)
+			v := NewLine(t[i], t[j]).IntersectHorizontal(h)
 			points = append(points, v)
 		}
 	}
 
 	return points
 }
+
+func (v *Vertex) read(r io.Reader) error {
+	var buf [8]byte
+	b := buf[:]
+	if _, err := io.ReadFull(r, b); err != nil {
+		return nil
+	}
+	v.x = math.Float64frombits(binary.LittleEndian.Uint64(b))
+	if _, err := io.ReadFull(r, b); err != nil {
+		return nil
+	}
+	v.y = math.Float64frombits(binary.LittleEndian.Uint64(b))
+	if _, err := io.ReadFull(r, b); err != nil {
+		return nil
+	}
+	v.z = math.Float64frombits(binary.LittleEndian.Uint64(b))
+	return nil
+}