Geometry Boost List: Re: [geometry] rtree nearest query with custom geometries

Subject: Re: [geometry] rtree nearest query with custom geometries
From: Adam Wulkiewicz (adam.wulkiewicz_at_[hidden])
Date: 2019-04-16 12:58:46

Hi Andrea,

Andrea Beconcini Via Geometry wrote:
> I am trying to use an rtree as an index to a set of triangles to 
> perform some spatial queries.
> The rtree stores std::pair<box, triangles> where box is the boost 
> geometry box.
>
> The problem occurs with the nearest query and, in particular, when two 
> or more elements have equivalent boxes,
> Â and I look for just one element, the result may be wrong.
>
> Look at the code below; the problem is that the two triangles have 
> equivalent bounding boxes, and since
> the query returns just one element, the result is the one I inserted 
> first. Even though the bounding boxes
> are the same, the two elements are not, I'd like the query to returns 
> t2 instead.
>
> I think I need to provide an IndexableGetter to my rtree, but according to
> https://www.boost.org/doc/libs/1_70_0/libs/geometry/doc/html/geometry/spatial_indexes/creation_and_modification.html
> the returned value has to be one of the Indexable concepts (Point, 
> Box, or Segment) and none of them seems to satisfy
> my requirements.
>
> Do I need to make my triangle Indexable? I could not find any 
> reference on how to do that and what methods are required
> for a type to be indexable; can anyone provide any resources that may 
> be useful?

No, only boxes should be used for indexing.

You have to iterate the query iterator and check a condition until 
you're satisfied with the result, e.g.:

double distance_to_closest_triangle = MAX;
for(auto it = rtree.qbegin(nearest(pt, rtree.size())) ; it != 
rtree.qend() ; ++it) {
 Â Â Â  if (distance_to_closest_triangle <= distance(pt, it->first))
 Â Â Â Â Â Â Â  break;
 Â Â Â  distance_to_closest_triangle = min(distance(pt, 
triangles[it->second]), distance_to_closest_triangle);
}

See also: 
https://www.boost.org/doc/libs/1_70_0/libs/geometry/doc/html/geometry/spatial_indexes/rtree_examples/iterative_query.html

Adam