
Geometry : 
Subject: [geometry] Question about boost::geometry::index::rtree and the nearest predicate
From: Branimir Betov (bbetov_at_[hidden])
Date: 20140122 16:23:49
Hi,
I posted in boostusers, but looks like this list is better. Sorry about
the double post.
I don't know if I don't understand how the rtree works or there is a
problem with the indexing.
I have an rtree with about 20,000 points and I tried creating two rtrees
with different strategies (linear and rstar) defined as follows:
typedef boost::geometry::model::point<double, 2,
boost::geometry::cs::spherical_equatorial<boost::geometry::degree>> point;
boost::geometry::index::rtree< point, boost::geometry::index::linear<16> >
coastPointsLinear;
boost::geometry::index::rtree< point, boost::geometry::index::rstar<16> >
coastPointsRStar;
When I query for the nearest 3 points, I get different results returned!
coastPointsRStar.query(bgi::nearest(point(latitude, longitude), 3),
std::back_inserter(nearestRStar));
coastPointsLinear.query(bgi::nearest(point(latitude, longitude), 3),
std::back_inserter(nearestLinear));
This seems like a bug. (I attached a text file with the list of the points
I put in the rtree; first two columns are longitude and latitude). The
results also seem to change if I change the maximum number of elements in
nodes from 16 to something else (i.e. 32, 64, etc.)
For what is worth, I also did an experiment with returning points in a box
and it seems like the intersects code returns the same points (works as I
expected) and they seem OK when I plot them in a GIS.
Please help me figure out what I might be doing wrong  here is the whole
test function.
namespace bgi = boost::geometry::index;
typedef boost::geometry::model::point<double, 2,
boost::geometry::cs::spherical_equatorial<boost::geometry::degree>> point;
boost::geometry::index::rtree< point, boost::geometry::index::linear<16> >
coastPointsLinear;
boost::geometry::index::rtree< point, boost::geometry::index::rstar<16> >
coastPointsRStar;
using namespace std;
void Test()
{
ifstream in("c:\\_Playground\\CoastPoints.txt");
CSVRow row;
while( in >> row )
{
double lat = atof(row[1].c_str());
double lon = atof(row[0].c_str());
coastPointsRStar.insert( point( lat, lon ));
coastPointsLinear.insert( point( lat, lon ));
}
in.close();
double longitude = 141.029209074;
double latitude = 38.2836106326;
vector<point> nearestRStar;
coastPointsRStar.query(bgi::nearest(point(latitude, longitude), 3),
std::back_inserter(nearestRStar));
PrintStats(longitude, latitude, nearestRStar, "RStar");
vector<point> nearestLinear;
coastPointsLinear.query(bgi::nearest(point(latitude, longitude), 3),
std::back_inserter(nearestLinear));
PrintStats(longitude, latitude, nearestLinear, "Linear");
}
Thank you
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