C++ Boost RTree overlaps does not work correctly - c++

Question

I am kinda confused and think I get something wrong but I really fail to see it.
I have a boost::geometry::index::rtree that stores 2D boxes of 2D geographic points. Now I try to check if a new box I add to that rtree overlaps with any box already in that rtree. And this check somehow fails for one test and I really don't get why because I do not believe the error is in the rtree/overlaps implementation.
My code is the following (in Visual Studio test environment):
using CoordinateSystem = boost::geometry::cs::geographic<boost::geometry::degree>;
using Point = boost::geometry::model::point<double, 2, CoordinateSystem>;
using RTreeBox = boost::geometry::model::box<Point>;
using RTreeEntry = std::pair<RTreeBox, uint64_t>;
constexpr static auto kRTreeMaxElementsPerNode = 4;
using RTreeAlgorithm = boost::geometry::index::rstar<kRTreeMaxElementsPerNode>;
using RTree = boost::geometry::index::rtree<RTreeEntry, RTreeAlgorithm>;
bool TestAddTreeEntry(RTree& tree, uint64_t index, RTreeBox box)
{
if (!boost::geometry::is_valid(box)) {
boost::geometry::correct(box);
}
std::vector<RTreeEntry> query_results;
tree.query(boost::geometry::index::overlaps(box), std::back_inserter(query_results));
if (query_results.size() > 0)
{
return false;
}
tree.insert(std::make_pair(box, index));
return true;
}
TEST_METHOD(test_rtree_mapping) {
RTree tree;
Assert::IsTrue(TestAddTreeEntry(tree, 1, RTreeBox({ 1, 1 }, { 3, 3 })));
Assert::IsTrue(TestAddTreeEntry(tree, 1, RTreeBox({ 4, 1 }, { 9, 5 })));
Assert::IsTrue(TestAddTreeEntry(tree, 1, RTreeBox({ 1, 4 }, { 2, 9 })));
Assert::IsFalse(TestAddTreeEntry(tree, 1, RTreeBox({ 1, 2.75 }, { 2, 9 })));
Assert::IsFalse(TestAddTreeEntry(tree, 1, RTreeBox({ 1, 4 }, { 3.5, 9 })));
}
The first Assert::IsFalse works - but also unexpectedly only overlaps with the first box ({1, 1}, {3, 3}) and not with the third one ({1, 4}, {2, 9}). The second Assert::IsFalse does not work because the entry is successfully added.
Anyone knows a reason behind this? Has this something to do with geographic coordinates that I do not understand yet?
Kind regards

Answer 1

Overlaps doesn't do what you expect. It's too strict. The docs state:
The function overlaps implements function Overlaps from the OGC Simple Feature Specification.
The OGC document contains:
That's admittedly hard to parse, but that's the nature of technical specifications. Luckily, intersects is much simpler:
a.Intersects(b) ⇔ ! a.Disjoint(b)
DEMO
I created a test program that
allows you to override the RELATION (e.g. bgi::intersects, bgi::overlaps, !bgi::disjoint)
also writes a SVG vizualtion of the shapes involved.
Live On Compiler Explorer
#include <boost/geometry.hpp>
#include <boost/geometry/index/rtree.hpp>
#include <fstream>
namespace bg = boost::geometry;
namespace bgm = bg::model;
namespace bgi = bg::index;
using CS = bg::cs::geographic<bg::degree>;
using Point = bg::model::point<double, 2, CS>;
using Box = bg::model::box<Point>;
using Tree = std::pair<Box, uint64_t>;
constexpr static auto kRTreeMaxElementsPerNode = 4;
using RTreeAlgorithm = bgi::rstar<kRTreeMaxElementsPerNode>;
using RTree = bgi::rtree<Tree, RTreeAlgorithm>;
#ifndef RELATION
#define RELATION bgi::intersects
#endif
#define RELATION_STR BOOST_PP_STRINGIZE(RELATION)
bool add(RTree& tree, uint64_t index, Box box) {
if (std::string reason; !bg::is_valid(box, reason)) {
std::cerr << "Trying to correct: " << bg::dsv(box) << " (" << reason << ")" << std::endl;
bg::correct(box);
assert(bg::is_valid(box));
}
for (auto it = qbegin(tree, RELATION(box)), e = qend(tree); it != e; ++it)
return false;
tree.insert(std::make_pair(box, index));
return true;
}
int main() {
std::cout << std::boolalpha;
RTree tree;
struct {
Box box;
char const* name;
char const* color;
} const shapes[]{
{{{1.00, 1.00}, {3.00, 3.00}}, "box1", "red"},
{{{4.00, 1.00}, {9.00, 5.00}}, "box2", "green"},
{{{1.00, 4.00}, {2.00, 9.00}}, "box3", "blue"},
{{{1.00, 2.75}, {2.00, 9.00}}, "probe1", "orange"},
{{{1.00, 4.00}, {3.50, 6.00}}, "probe2", "gray"},
};
for (auto const& s : shapes) {
auto idx = (&s - shapes);
auto added = add(tree, idx, s.box);
std::cout << "Adding " << s.name << " as #" << idx << ": "
<< (added ? "ACCEPT" : "REJECTED") << " " << bg::dsv(s.box)
<< "\n";
if (!added) {
for (auto it = qbegin(tree, RELATION(s.box)), e = qend(tree); it != e; ++it) {
std::cout << " - because " << s.name << " " << RELATION_STR
<< " " << shapes[it->second].name << "\n";
}
}
}
{
std::ofstream ofs("output.svg");
bg::svg_mapper<Point> svg(ofs, 400, 400);
auto style = [](std::string c) {
return "fill-rule:nonzero;fill-opacity:0.25;fill:" + c +
";stroke:" + c + ";stroke-width:1;";
};
for (auto const& [b, name, color] : shapes) {
svg.add(b);
}
for (auto const& [b, name, color] : shapes) {
auto h = b.max_corner().get<1>() - b.min_corner().get<1>();
auto mc = b.max_corner();
mc.set<1>(mc.get<1>() - h / 2);
svg.text(mc,
name +
("\n" + boost::lexical_cast<std::string>(bg::dsv(b))),
style(color));
}
for (auto const& [b, _, color] : shapes)
svg.map(b, style(color));
}
}
With either -DRELATION=bgi::intersects or -DRELATION=!bgi::disjoint:
Adding box1 as #0: ACCEPT ((1, 1), (3, 3))
Adding box2 as #1: ACCEPT ((4, 1), (9, 5))
Adding box3 as #2: ACCEPT ((1, 4), (2, 9))
Adding probe1 as #3: REJECTED ((1, 2.75), (2, 9))
- because probe1 bgi::intersects box1
- because probe1 bgi::intersects box3
Adding probe2 as #4: REJECTED ((1, 4), (3.5, 6))
- because probe2 bgi::intersects box3
(replacing bgi::intersects with !bgi::disjoint in the output obviously).
Visualization:
Note how the output changes if you change probe1:
{{{1.00, 2.75}, {1.50, 9.00}}, "probe1", "orange"},
That looks like:
This would behave as you expected even with the bgi::overlaps. Overlaps is just too strict for the expectated output.