--- a/pkg/octree/vertex.go	Fri Oct 05 18:46:13 2018 +0200
+++ b/pkg/octree/vertex.go	Sat Oct 06 13:20:31 2018 +0200
@@ -294,20 +294,26 @@
 
 func (mls MultiLineStringZ) AsWKB() []byte {
 
-	var buf bytes.Buffer
+	// pre-calculate size to avoid reallocations.
+	size := 1 + 4 + 4
+	for _, ml := range mls {
+		size += 1 + 4 + 4 + len(ml)*3*8
+	}
 
-	binary.Write(&buf, binary.LittleEndian, wkbNDR)
-	binary.Write(&buf, binary.LittleEndian, wkbMultiLineStringZ)
-	binary.Write(&buf, binary.LittleEndian, uint32(len(mls)))
+	buf := bytes.NewBuffer(make([]byte, 0, size))
+
+	binary.Write(buf, binary.LittleEndian, wkbNDR)
+	binary.Write(buf, binary.LittleEndian, wkbMultiLineStringZ)
+	binary.Write(buf, binary.LittleEndian, uint32(len(mls)))
 
 	for _, ml := range mls {
-		binary.Write(&buf, binary.LittleEndian, wkbNDR)
-		binary.Write(&buf, binary.LittleEndian, wkbLineStringZ)
-		binary.Write(&buf, binary.LittleEndian, uint32(len(ml)))
+		binary.Write(buf, binary.LittleEndian, wkbNDR)
+		binary.Write(buf, binary.LittleEndian, wkbLineStringZ)
+		binary.Write(buf, binary.LittleEndian, uint32(len(ml)))
 		for _, p := range ml {
-			binary.Write(&buf, binary.LittleEndian, math.Float64bits(p.X))
-			binary.Write(&buf, binary.LittleEndian, math.Float64bits(p.Y))
-			binary.Write(&buf, binary.LittleEndian, math.Float64bits(p.Z))
+			binary.Write(buf, binary.LittleEndian, math.Float64bits(p.X))
+			binary.Write(buf, binary.LittleEndian, math.Float64bits(p.Y))
+			binary.Write(buf, binary.LittleEndian, math.Float64bits(p.Z))
 		}
 	}