W dniu 23.05.2021 o 17:33, Adam Wulkiewicz pisze:
W dniu 18.05.2021 o 09:34, Jens Thiele via Boost-users pisze:
I have lots of linestrings and want to find the k nearest linestrings to
some point.
Looking at the example
/libs/geometry/doc/index/src/examples/rtree/polygons_shared_ptr.cpp
I first thought this should be close to the solution and I just could
replace the polygons with linestrings. But now I think the nearest query
in that example only finds the nearest polygon bounding boxes and not
the nearest polygons. Am I correct?
If yes, how would one extend that example to find the nearest polygons?
Hi Jens,
Yes, your understanding is correct. Bounding boxes of polygons
together with pointers to polygons are stored in the rtree. This is
also what is returned by the query. So you need to calculate the
distances to actual linestrings by yourself.
I propose you to use query iterators instead of query function. Then
you can iterate over nearest boxes (passing the number of values
stored in the rtree into the nearest predicate). In the loop calculate
distances to linestrings and break when you have enough of them. You
should probably break when the number of linestrings you have is equal
to your K and the distance to the furthest linestring is lesser than
the distance to the current box returned by the rtree query (because
then you know that you will not get any closer linestring). To track
the furthest linestring you can use std::priority_queue.
Adam
Correction: "the current box returned by the rtree query"
I of course had in mind: "the current box returned by the query iterator"
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