Geometry Boost List: Re: [geometry] Nsphere Usage

From: Adam Wulkiewicz (adam.wulkiewicz_at_[hidden])
Date: 2020-03-06 18:28:01

Hi Dinos,

W dniu 05.03.2020 o 17:21, Dinos Lampropoulos via Geometry pisze:
> Dear all,
>
> I am trying to use nsphere to query an rtree with a circle with a 
> standard radius. First of all, I was unable to import nsphere. I 
> looked at the directory where boost is installed and I couldn't find a 
> folder named "extensions". How can I use nsphere? Is there another way 
> to achieve my goal without using nsphere?

I answered this question already at GitHub but for people reading the 
mailing list I'm pasting the answer here too.

Extensions only exist in the develop branch of Boost.Geometry so you 
either has to clone the git repo or copy the code from the develop 
branch and make sure it works well with your version of Boost.

A workaround would be to create a box enclosing the circle and use 
bgi::satisfies to filter out the elements that are outside of it while 
performing the query, so something like:

 Â Â Â  template <typename T> inline T sqr(T const& v) { return v * v; }

 Â Â Â  // ...

 Â Â Â  box_type box{{center_x - r, center_y - r}, {center_x + r, center_y 
+ r}};
 Â Â Â  double r_sqr = sqr(r);
 Â Â Â  rtree.query(bgi::intersects(box) && bgi::satisfies([](auto const& 
pt_elem) {
 Â Â Â  Â Â Â  return sqr(bg::get<0>(pt_elem) - center_x) + 
sqr(bg::get<1>(pt_elem) - center_y) <= r_sqr;
 Â Â Â  }), std::back_inserter(result));

Adam