Fade library Delaunay Triangulation site neighbors

Question

In the Delaunay triangulation using Fade library it is possible to visit incident triangle to a site and visit its neighbors as explained here: http://www.geom.at/example2-traversing/

I could not figure how to traverse the site neighbor-sites by exploiting the incident triangle and its neighbors. Which triangle neighbor should I visit at each iteration to accomplish this?

In the below example, the main site is in the blue circle, and I want to save all the neighbor sites in the red circles in some array. .

example

Answer 1

I'm the author of Fade2D. It is much easier when you use the TriangleAroundVertexIterator or the Fade_2D::getIncidentTriangles() method, see the demo function below: It creates a random triangulation, extracts for a certain point the surrounding vertices and draws the result:

vector<Point2> vRandomPoints;
generateRandomPoints(50,0,1000,vRandomPoints,1);

Fade_2D dt;
vector<Point2*> vVertexHandles;
dt.insert(vRandomPoints,vVertexHandles);

// Your point index to be checked and the corresponding pointer
size_t pointToCheck=5;
Point2* pVertexToCheck(vVertexHandles[pointToCheck]);

// Fetch the incident triangles
std::vector<Triangle2*> vIncidentTriangles;
dt.getIncidentTriangles(pVertexToCheck,vIncidentTriangles);

// Extract the vertices
set<Point2*> sResultVertices;
for(std::vector<Triangle2*>::iterator it(vIncidentTriangles.begin());
    it!=vIncidentTriangles.end();++it)
{
    Triangle2* pIncidentT(*it);
    int intraTriangleIndex(pIncidentT->getIntraTriangleIndex(pVertexToCheck));
    sResultVertices.insert(pIncidentT->getCorner((intraTriangleIndex+1)%3));
    sResultVertices.insert(pIncidentT->getCorner((intraTriangleIndex+2)%3));
}
cout<<"number of points: "<<sResultVertices.size()<<endl;

// Verify: Postscript Visualization
Visualizer2 vis("result.ps");
dt.show(&vis,false);
vis.addObject(Label(*pVertexToCheck,"base"),Color(CGREEN));
for(set<Point2*>::iterator it(sResultVertices.begin());it!=sResultVertices.end();++it)
{
    vis.addObject(Label(**it,"VTX"),Color(CRED));
}
vis.writeFile();