/// <summary>
/// creates the concave hull based on the convex hull and an angle threshold
/// </summary>
/// <param name="pConvexEdges">edges of convex hull</param>
/// <param name="pPoints">the point cloud data set</param>
/// <param name="pMaxAngle">angle threshold</param>
/// <returns>list of concave hull edges</returns>
static List <tEdge> CreateConvaveHullFromConvexEdges(List <DefaultConvexFace <Vertex> > pConvexEdges, HashSet <Vertex> pPoints, double pMaxAngle)
{
//initialize arrays
List <tEdge> convexHull = new List <tEdge>();
foreach (var v in pConvexEdges)
{
convexHull.Add(new tEdge(v.Vertices[0], v.Vertices[1]));
}
List <tEdge> concaveHull = new List <tEdge>();
//iterate through convex hull until concave hull is found
while (convexHull.Count > 0)
{
//find longest edge in convex hull list
tEdge longestEdge = convexHull.MaxBy(t => t.length);
//remove longest edge from convex hull
convexHull.Remove(longestEdge);
//find nearest point
List <tEdge> edges = convexHull.Concat(concaveHull).ToList();
tVector nextPoint = FindPointWithSmallestAngle(pPoints, longestEdge, edges, pMaxAngle);
if (nextPoint == null) //if no next point found
{
concaveHull.Add(longestEdge);
continue;
}
//create edges based on nearest point
tEdge e2 = new tEdge(longestEdge.v1, nextPoint.vector);
tEdge e3 = new tEdge(longestEdge.v2, nextPoint.vector);
//check if e2 and e3 intersect
bool intersect = false;
foreach (tEdge e1 in edges)
{
if (Intersects(e2, e1) || Intersects(e3, e1))
{
intersect = true;
break;
}
}
//add e2 and e3 to List A again, if no intersection
if (intersect == false)
{
convexHull.Add(e2); convexHull.Add(e3); continue;
}
//if no concaviction found, add longest edge to concaveHull list
concaveHull.Add(longestEdge);
}
return(concaveHull);
}
/// <summary>
/// finds the point with the smallest angle from a given dataset towards an edge
/// </summary>
/// <param name="pPoints">the dataset</param>
/// <param name="pLine">the edge to calculate the angle towards</param>
/// <param name="pBoundaries">boundaries</param>
/// <param name="pMaxAngle">angle threshold</param>
/// <returns></returns>
static tVector FindPointWithSmallestAngle(HashSet <Vertex> pPoints, tEdge pLine, List <tEdge> pBoundaries, double pMaxAngle)
{
tVector bestFit = null;
Object lockObject = new object();
Parallel.ForEach(pPoints, v =>
{
//check if point is on concave hull
if (!IsPointOnConcaveHull(v, pBoundaries))
{
//calculate new potential edges
tEdge t1 = new tEdge(pLine.v1, v);
tEdge t2 = new tEdge(pLine.v2, v);
//check if local maximum < edge length
if (t1.length < pLine.length && t2.length < pLine.length)
{
//calculate the highest angle between lines and the new point
double maxAngle;
double angleA = Math.Abs(CalculateAngleBetweenTwoLines(pLine, t1));
double angleB = Math.Abs(CalculateAngleBetweenTwoLines(pLine, t2));
if (angleA > angleB)
{
maxAngle = angleA;
}
else
{
maxAngle = angleB;
}
//check if highest angle is smaller than threshold
if (maxAngle < pMaxAngle)
{
//check if bestFit has been initialized
tVector currentFit = new tVector(v, maxAngle);
lock (lockObject)
if (bestFit == null)
{
bestFit = currentFit;
}
//check if current point has a better fit
lock (lockObject)
if (currentFit.maxAngle < bestFit.maxAngle)
{
bestFit = currentFit;
}
}
}
}
});
return(bestFit);
}
