diff --git a/vtm/src/org/oscim/core/Box.java b/vtm/src/org/oscim/core/Box.java
index 08c16836..b089eef0 100644
--- a/vtm/src/org/oscim/core/Box.java
+++ b/vtm/src/org/oscim/core/Box.java
@@ -1,5 +1,6 @@
 /*
  * Copyright 2013 Hannes Janetzek
+ * Copyright 2018 Gustl22
  *
  * This file is part of the OpenScienceMap project (http://www.opensciencemap.org).
  *
@@ -33,6 +34,17 @@ public class Box {
 
     }
 
+    /**
+     * Simple box instantiation (for adding extents).
+     *
+     * @param x the initial x value
+     * @param y the initial y value
+     */
+    public Box(double x, double y) {
+        this.xmax = this.xmin = x;
+        this.ymax = this.ymin = y;
+    }
+
     /**
      * Instantiates a new Box.
      *
@@ -50,6 +62,9 @@ public class Box {
         this.ymax = ymax;
     }
 
+    /**
+     * Copy constructor.
+     */
     public Box(Box bbox) {
         this.xmin = bbox.xmin;
         this.ymin = bbox.ymin;
@@ -129,7 +144,7 @@ public class Box {
     }
 
     /**
-     * convrt map coordinates to lat/lon.
+     * Convert map coordinates to lat/lon.
      */
     public void map2mercator() {
         double minLon = MercatorProjection.toLongitude(xmin);
@@ -156,12 +171,27 @@ public class Box {
         ymax *= d;
     }
 
+    /**
+     * Init or overwrite extents of box.
+     *
+     * @param points the points to extend to
+     */
     public void setExtents(float[] points) {
+        setExtents(points, points.length);
+    }
+
+    /**
+     * Init or overwrite extents of box.
+     *
+     * @param points the points to extend to
+     * @param length the number of considered points
+     */
+    public void setExtents(float[] points, int length) {
         float x1, y1, x2, y2;
         x1 = x2 = points[0];
         y1 = y2 = points[1];
 
-        for (int i = 2, n = points.length; i < n; i += 2) {
+        for (int i = 2; i < length; i += 2) {
             float x = points[i];
             if (x < x1)
                 x1 = x;
diff --git a/vtm/src/org/oscim/layers/tile/buildings/S3DBLayer.java b/vtm/src/org/oscim/layers/tile/buildings/S3DBLayer.java
index 93b0cee5..77ed8959 100644
--- a/vtm/src/org/oscim/layers/tile/buildings/S3DBLayer.java
+++ b/vtm/src/org/oscim/layers/tile/buildings/S3DBLayer.java
@@ -112,7 +112,7 @@ public class S3DBLayer extends BuildingLayer {
                 float p1 = element.points[k];
                 float p2 = element.points[k + 1];
                 if (bb == null)
-                    bb = new Box(p1, p2, p1, p2);
+                    bb = new Box(p1, p2);
                 else {
                     bb.add(p1, p2);
                 }