Fix the incorrectly computed normal

The normal should take into account all of the points, not just the
first 3. the change allows for polygons whs first 3 points may in fact
be in a line producing an invalid normal

src/main/java/eu/mihosoft/vrl/v3d/Polygon.java

@@ -348,10 +348,8 @@ public Polygon transform(Transform transform) {
         );
 
         Vector3d a = this.vertices.get(0).pos;
-        Vector3d b = this.vertices.get(1).pos;
-        Vector3d c = this.vertices.get(2).pos;
 
-        this.plane.normal = b.minus(a).cross(c.minus(a)).normalized();
+        this.plane.normal = computeNormal();
         this.plane.dist = this.plane.normal.dot(a);
 
         if (transform.isMirror()) {
@@ -361,7 +359,21 @@ public Polygon transform(Transform transform) {
         }
         return this;
     }
+    public Vector3d computeNormal() {
+        Vector3d normal = new Vector3d(0, 0, 0);
+        int n = this.vertices.size();
+
+        for (int i = 0; i < n; i++) {
+            Vector3d current = this.vertices.get(i).pos;
+            Vector3d next = this.vertices.get((i + 1) % n).pos;
+
+            normal.x += (current.y - next.y) * (current.z + next.z);
+            normal.y += (current.z - next.z) * (current.x + next.x);
+            normal.z += (current.x - next.x) * (current.y + next.y);
+        }
 
+        return normal.normalized();
+    }
     /**
      * Returns a transformed copy of this polygon.
      *

src/test/java/eu/mihosoft/vrl/v3d/SVGLoadTest.java

@@ -13,7 +13,15 @@
 import eu.mihosoft.vrl.v3d.svg.SVGLoad;
 
 public class SVGLoadTest {
-
+	@Test
+	public void adversarial() throws IOException {
+		File svg = new File("Part-Num-0.svg");
+		if(!svg.exists())
+			throw new RuntimeException("Test file missing!"+svg.getAbsolutePath());
+		SVGLoad s = new SVGLoad(svg.toURI());
+		run(s);
+		//fail("Not yet implemented");
+	}
 	@Test
 	public void test() throws IOException {
 		File svg = new File("Test.SVG");
@@ -45,5 +53,7 @@ private ArrayList<Object>  run(SVGLoad s) {
 
 		return polys;
 	}
+
+
 
 }