--- a/pkg/octree/triangulation.go	Wed Jun 05 16:34:52 2019 +0200
+++ b/pkg/octree/triangulation.go	Wed Jun 05 18:17:01 2019 +0200
@@ -43,6 +43,29 @@
 }
 
 func (t *Triangulation) ConcaveHull(tooLong float64) []int32 {
+	var (
+		minX float64 = math.MaxFloat64
+		minY float64 = math.MaxFloat64
+		maxX float64 = -math.MaxFloat64
+		maxY float64 = -math.MaxFloat64
+	)
+
+	linear := func(x1, y1, x2, y2 float64) func(float64) float64 {
+		// y1 = x1*m + b
+		// y2 = x2*m + b
+		// b = y1 - x1*m
+		// y1-y2 = (x1-x2)*m
+		// m = (y1-y2)/(x1-x2) for x1 != x2
+
+		if x1 == x2 {
+			return func(float64) float64 { return (y1 + y2) * 0.5 }
+		}
+
+		m := (y1 - y2) / (x1 - x2)
+		b := y1 - x1*m
+
+		return func(x float64) float64 { return m*x + b }
+	}
 
 	tooLong *= tooLong
 
@@ -76,10 +99,53 @@
 		return false
 	}
 
+	for _, i := range candidates {
+		vs := t.Triangles[i*3 : i*3+3]
+		for _, vj := range vs {
+			p := t.Points[vj]
+			minX = math.Min(p.X, minX)
+			maxX = math.Max(p.X, maxX)
+			minY = math.Min(p.Y, minY)
+			maxY = math.Max(p.Y, maxY)
+		}
+	}
+
+	xf := linear(minX, 0, maxX, 1500)
+	yf := linear(minY, 1500, maxY, 0)
+
+	f, err := os.Create("/tmp/prehull.svg")
+	if err == nil {
+		canvas := svg.New(f)
+		canvas.Start(1500, 1500)
+
+		for _, i := range candidates {
+			var style string
+			if isBorder(i) {
+				style = "stroke:red"
+			} else {
+				style = "stroke:black"
+			}
+			vs := t.Triangles[i*3 : i*3+3]
+			for j, vj := range vs {
+				p0 := t.Points[vj]
+				p1 := t.Points[vs[(j+1)%3]]
+
+				x1 := int(math.Floor(xf(p0.X)))
+				y1 := int(math.Floor(yf(p0.Y)))
+				x2 := int(math.Floor(xf(p1.X)))
+				y2 := int(math.Floor(yf(p1.Y)))
+				canvas.Line(x1, y1, x2, y2, style)
+			}
+
+		}
+		canvas.End()
+		f.Close()
+	}
+
 	var newCandidates []int32
 
+	log.Printf("info: candidates: %d\n", len(candidates))
 	for len(candidates) > 0 {
-		log.Printf("info: candidates: %d\n", len(candidates))
 
 		oldRemoved := len(removed)
 
@@ -114,6 +180,7 @@
 		for j := int32(0); j < 3; j++ {
 			e := n + j
 			if t.Halfedges[e] < 0 || removed[e/3] {
+				//if t.Halfedges[e] < 0 {
 				edges = append(edges, [2]int32{
 					t.Triangles[e],
 					t.Triangles[n+(j+1)%3],
@@ -126,50 +193,12 @@
 		fmt.Printf("%d - %d\n", edges[i][0], edges[i][1])
 	}
 
+	log.Printf("num vertices: %d\n", len(t.Points))
+
 	log.Printf("num of border triangles: %d\n", len(edges))
 	log.Printf("len convex hull: %d\n", len(t.ConvexHull))
 
-	var (
-		minX float64 = math.MaxFloat64
-		minY float64 = math.MaxFloat64
-		maxX float64 = -math.MaxFloat64
-		maxY float64 = -math.MaxFloat64
-	)
-
-	for i := range edges {
-		p0 := t.Points[edges[i][0]]
-		p1 := t.Points[edges[i][1]]
-
-		minX = math.Min(p0.X, minX)
-		maxX = math.Max(p0.X, maxX)
-		minY = math.Min(p0.Y, minY)
-		maxY = math.Max(p0.Y, maxY)
-
-		minX = math.Min(p1.X, minX)
-		maxX = math.Max(p1.X, maxX)
-		minY = math.Min(p1.Y, minY)
-		maxY = math.Max(p1.Y, maxY)
-	}
-	linear := func(x1, y1, x2, y2 float64) func(float64) float64 {
-		// y1 = x1*m + b
-		// y2 = x2*m + b
-		// b = y1 - x1*m
-		// y1-y2 = (x1-x2)*m
-		// m = (y1-y2)/(x1-x2) for x1 != x2
-
-		if x1 == x2 {
-			return func(float64) float64 { return (y1 + y2) * 0.5 }
-		}
-
-		m := (y1 - y2) / (x1 - x2)
-		b := y1 - x1*m
-
-		return func(x float64) float64 { return m*x + b }
-	}
-	xf := linear(minX, 0, maxX, 1499)
-	yf := linear(minY, 0, maxY, 1499)
-
-	f, err := os.Create("/tmp/hull.svg")
+	f, err = os.Create("/tmp/hull.svg")
 	if err == nil {
 
 		canvas := svg.New(f)
@@ -188,6 +217,7 @@
 		canvas.End()
 		f.Close()
 	}
+	log.Println("after draw")
 	return nil
 }