From efd9d1260d8164a20821cf8645f78e3d57dac9ee Mon Sep 17 00:00:00 2001
From: "SND\\wo80_cp" <SND\wo80_cp@0e2699bc-83d4-4a8f-98e7-55e24ab8c7a5>
Date: Thu, 9 Jul 2015 17:20:03 +0000
Subject: [PATCH] Add a simple polygon validator.

git-svn-id: https://triangle.svn.codeplex.com/svn@77032 0e2699bc-83d4-4a8f-98e7-55e24ab8c7a5
---
 .../Triangle/Tools/PolygonValidator.cs        | 164 ++++++++++++++++++
 Triangle.NET/Triangle/Triangle.csproj         |   1 +
 2 files changed, 165 insertions(+)
 create mode 100644 Triangle.NET/Triangle/Tools/PolygonValidator.cs

diff --git a/Triangle.NET/Triangle/Tools/PolygonValidator.cs b/Triangle.NET/Triangle/Tools/PolygonValidator.cs
new file mode 100644
index 0000000..da1da08
--- /dev/null
+++ b/Triangle.NET/Triangle/Tools/PolygonValidator.cs
@@ -0,0 +1,164 @@
+// -----------------------------------------------------------------------
+// <copyright file="PolygonValidator.cs">
+// Triangle.NET code by Christian Woltering, http://triangle.codeplex.com/
+// </copyright>
+// -----------------------------------------------------------------------
+
+namespace TriangleNet.Tools
+{
+    using System;
+    using TriangleNet.Geometry;
+
+    public static class PolygonValidator
+    {
+        /// <summary>
+        /// Test the polygon for consistency.
+        /// </summary>
+        public static bool IsConsistent(IPolygon poly)
+        {
+            var logger = Log.Instance;
+
+            int horrors = 0;
+
+            int i = 0;
+            int count = poly.Points.Count;
+
+            foreach (var p in poly.Points)
+            {
+                if (p == null)
+                {
+                    horrors++;
+                    logger.Warning(String.Format("Point {0} is null.", i), "PolygonValidator.IsConsistent()");
+                }
+                else if (double.IsNaN(p.x + p.y) || double.IsInfinity(p.x + p.y))
+                {
+                    horrors++;
+                    logger.Warning(String.Format("Point {0} has invalid coordinates.", i), "PolygonValidator.IsConsistent()");
+                }
+                i++;
+            }
+
+            i = 0;
+
+            foreach (var seg in poly.Segments)
+            {
+                if (seg == null)
+                {
+                    horrors++;
+                    logger.Warning(String.Format("Segment {0} is null.", i), "PolygonValidator.IsConsistent()");
+                }
+                else
+                {
+                    if (seg.P0 < 0 || seg.P0 >= count)
+                    {
+                        horrors++;
+                        logger.Warning(String.Format("Segment {0} has invalid startpoint.", i),
+                            "PolygonValidator.IsConsistent()");
+                    }
+
+                    if (seg.P1 < 0 || seg.P1 >= count)
+                    {
+                        horrors++;
+                        logger.Warning(String.Format("Segment {0} has invalid endpoint.", i),
+                            "PolygonValidator.IsConsistent()");
+                    }
+                }
+
+                i++;
+            }
+
+            return horrors == 0;
+        }
+
+        /// <summary>
+        /// Test the polygon for duplicate vertices.
+        /// </summary>
+        public static bool HasDuplicateVertices(IPolygon poly)
+        {
+            var logger = Log.Instance;
+
+            int horrors = 0;
+
+            var points = poly.Points.ToArray();
+
+            (new PointSorter()).Sort(points);
+
+            for (int i = 1; i < points.Length; i++)
+            {
+                if (points[i - 1] == points[i])
+                {
+                    horrors++;
+                    logger.Warning(String.Format("Found duplicate point {0}.", points[i]),
+                        "PolygonValidator.HasDuplicateVertices()");
+                }
+            }
+
+            return horrors == 0;
+        }
+
+        /// <summary>
+        /// Test the polygon for 360 degree angles.
+        /// </summary>
+        public static bool HasBadAngles(IPolygon poly)
+        {
+            var logger = Log.Instance;
+
+            int horrors = 0;
+            int i = 0;
+
+            Point p0 = null, p1 = null;
+            Point q0, q1;
+
+            int count = poly.Points.Count;
+
+            foreach (var seg in poly.Segments)
+            {
+                q0 = p0;
+                q1 = p1;
+
+                p0 = (seg.P0 >= 0 && seg.P0 < count) ? poly.Points[seg.P0] : null;
+                p1 = (seg.P1 >= 0 && seg.P1 < count) ? poly.Points[seg.P1] : null;
+
+                if (q0 != null && q1 != null)
+                {
+                    // The two segments are connected.
+                    if (p0 == q1 && p1 != null)
+                    {
+                        if (IsBadAngle(q0, p0, p1))
+                        {
+                            horrors++;
+                            logger.Warning(String.Format("Bad segment angle found at index {0}.", i),
+                                "PolygonValidator.HasBadAngles()");
+                        }
+                    }
+                }
+
+                i++;
+            }
+
+            return horrors == 0;
+        }
+
+        private static bool IsBadAngle(Point a, Point b, Point c, double eps = 0.0)
+        {
+            double x = DotProduct(a, b, c);
+            double y = CrossProductLength(a, b, c);
+
+            return Math.Abs(Math.Atan2(y, x)) <= eps;
+        }
+
+        //  Returns the dot product <AB, BC>.
+        private static double DotProduct(Point a, Point b, Point c)
+        {
+            //  Calculate the dot product.
+            return (a.X - b.X) * (c.X - b.X) + (a.Y - b.Y) * (c.Y - b.Y);
+        }
+
+        //  Returns the length of cross product AB x BC.
+        private static double CrossProductLength(Point a, Point b, Point c)
+        {
+            //  Calculate the Z coordinate of the cross product.
+            return (a.X - b.X) * (c.Y - b.Y) - (a.Y - b.Y) * (c.X - b.X);
+        }
+    }
+}
diff --git a/Triangle.NET/Triangle/Triangle.csproj b/Triangle.NET/Triangle/Triangle.csproj
index a5c1417..7dd5d81 100644
--- a/Triangle.NET/Triangle/Triangle.csproj
+++ b/Triangle.NET/Triangle/Triangle.csproj
@@ -60,6 +60,7 @@
     <Compile Include="Meshing\Data\BadSubseg.cs" />
     <Compile Include="Meshing\Data\BadTriangle.cs" />
     <Compile Include="Tools\IntersectionHelper.cs" />
+    <Compile Include="Tools\PolygonValidator.cs" />
     <Compile Include="Topology\DCEL\DcelMesh.cs" />
     <Compile Include="Topology\Osub.cs" />
     <Compile Include="Topology\Otri.cs" />