Re: [Boost-users] can not compile nearest neighbors in d dimensions

Georgios Samaras wrote:

Thanks for the replies, now it is clearer. However, the minimum dimension I have in my datasets is 100 and I want to run NN with dimension 10000.

So, how I am going to initialize a point?

template <int CompileTimeDimension> void fill(point& tmp) { for(int j = CompileTimeDimension - 1 ; j >= 0 ; --j) { bg::set<CompileTimeDimension-->(tmp, 5); } }

Even I can see that the above code won't even compile. Writting manually bg::set<0>(tmp, 5), ..., bg::set<10000>(tmp, 5) does not really sound a good idea. So what should I do?

Maybe boost nearest's neighbors are meant to be used in higher dimensions?

I'm curious about the result! I didn't test Boost.Geometry for such big dimensions. One point will take 40kB, right? 1M of points would require 40 GB of memory. I'm wondering how big will be the difference in performance of e.g. simple searching in std::vector in O(N) vs rtree kNN. How many points do you want to store in the rtree? If the number is too small you may not see the difference. In order to handle arbitrary dimensions (more or less) you might replace the for-loop with the compile-time recursive template (see the code below). Assuming the compiler would be able to compile it (it will take some time). E.g. VS2010 stops on CompileTimeDimension=3030 with the "error C1001: An internal error has occurred in the compiler" and a note: "compiler is out of heap space". It probably would be possible to somehow increase it with some compler parameter but I wouldn't recommend it. So if you're sure that you're unable to specify some dimensions for which your program should work or at least make the possible range of dimensions shorter, e.g. you know that there can only be {100, 1000, 10000} or at least [100, 200, 300, ... 10000], then Boost.Geometry is probably not suitable for you needs. Or maybe someone else has some other idea? #include #include #include namespace bg = boost::geometry; namespace bgi = boost::geometry::index; template <int CompileTimeDimension> void do_something() { typedef bg::model::point point; bgi::rtree > rt; } template struct do_something_for_dimension { static void apply(int run_time_dimension) { if ( run_time_dimension == CompileTimeDimension ) do_something<CompileTimeDimension>(); else do_something_for_dimension::apply(run_time_dimension); } }; // specialization to break the compile-time recursion template <int Max> struct do_something_for_dimension { static void apply(int) { throw std::runtime_error("run-time dimension not found!"); } }; int main() { int run_time_dimension = 1000; if ( run_time_dimension < 100 || run_time_dimension >= 10001 ) std::cerr << "invalid dimension!"; else do_something_for_dimension<100, 10001>::apply(run_time_dimension); } Regards, Adam