Removing point from cloud which are closer than threshold distance

Question

I am importing mesh file where each face is described by coordinates of its vertices. Most vertices are shared between points. Therefore, I would like to eliminate points which are closer than threshold to a point which has been already added to the cloud. That means that I need to efficiently perform closest-point lookup and point insertion at the same time.

I try to use vtkPointLocator which I've already used for static cloud; but I am at loss how is it supposed to be used incrementally. The documentation is quite terse, and examples (e.g. this one) don't cover this scenario. This post was somewhat helpful, but I still don't have a working solution - I get segfaults in InsertNextPoint (the case below), infinite recursion in CheateChildNode (when using vtkIncrementalOctreePointLocator instead of vtkPointLocator), or some VTK error (like no points to subdivide, when there are zero points).

This is approximately what I do:

// read from input file
std::vector<Vector3d> vertices;
// bounds of the data are known    
double bounds[6]={/*...*/}; 

const double threshold=1e-5;

auto locator=vtkSmartPointer<vtkIncrementalOctreePointLocator>::New();
auto polydata=vtkSmartPointer<vtkPolyData>::New();
auto points=vtkSmartPointer<vtkPoint>::New();

polydata->SetPoints(points);
locator->SetDataSet(polydata);
locator->InitPointInsertion(points,bounds);

for(size_t i=0; i< i<vertices.size(); i++){
    double* vertex=vertices[i].data(); // pointer to data
    double dist; // unused
    vtkIdType id;
    // don't search if there are no points yet
    // FindClosestPointWithinRadius calls BuildLocator internally,
    // which needs some points to be present already
    if(points->GetNumberOfPoints()>0) id=locator->FindClosestPointWithinRadius(threshold,vertex,dist);
    else id=-1;
    if(id<0){
        // point not found, insert it into the locator
        locator->InsertNextPoint(vertex);
    }
}

If there is an obvious error in the way the error is organized, I will be happy for any suggestion. If not, I try to make a MWE.

From reading the source, it seems even incremental classes call BuildLocator at every lookup, if the pointset was modified, which might be expensive. A suggestion for a better class for combined insertion/lookup would be therefore also appreciated.

Answer 1

If I'm understanding your problem correctly, you may want to look at vtkCleanPolyData, with PointMergingOn and a given tolerance.