[英]Boost geometry returning inconsistent results for intersects and intersection
In my application I'm using boost geometry to perform mainly intersection and difference calculations.在我的应用程序中,我使用 boost 几何来主要执行交集和差异计算。 Unfortunately I noticed an inconsistency in the results of:
不幸的是,我注意到结果不一致:
What I do is:我要做的是:
#include <iostream>
#include <boost/geometry.hpp>
namespace bg = boost::geometry;
using point_t = bg::model::d2::point_xy<double>;
using polygon_t = bg::model::polygon<point_t>;
using mpolygon_t = bg::model::multi_polygon<polygon_t>;
int main()
{
polygon_t poly1, poly2;
mpolygon_t poly3, poly4, poly5;
bg::read_wkt("POLYGON(("
"12227.0 4967.0000000000009, 12238.0 4967.0000000000009, "
"12238.0 4813.0000000000009, 12227.0 4813.0000000000009, "
"12227.0 4967.0000000000009))", poly1);
bg::read_wkt("POLYGON(("
"12254.0 4947.0, 12219.0 4982.0, 12219.0 5020.0, 12254.0 5055.0, "
"12261.0 5055.0, 12263.0 5055.0, 12283.0 5055.0, 12283.0 4947.0, "
"12263.0 4947.0, 12261.0 4947.0, 12254.0 4947.0))", poly2);
bg::intersection(poly1, poly2, poly3);
bg::difference(poly1, poly3[0], poly4);
// b0 = true, b1 = false
bool b0 = bg::intersects(poly2, poly4[0]);
bool b1 = bg::intersection(poly2, poly4, poly5) && (poly5.size() != 0);
bool b2 = !bg::disjoint(poly2, poly4[0]) && !bg::touches(poly2, poly4[0]);
bool b3 = bg::overlaps(poly2, poly4[0]) || bg::within(poly4[0], poly2) || bg::within(poly2, poly4[0]);
std::cout << b0 << b1 << b2 << b3 << std::endl;
return 1;
}
The weird thing is that bg::intersects returns true while bg::intersection returns an empty intersection.奇怪的是 bg::intersects 返回 true 而 bg::intersection 返回一个空的交集。
Does anyone have an idea why this happens?有谁知道为什么会这样? (Maybe accuracy problem?) and even more interesting: How can I avoid such problems?
(也许是准确性问题?)甚至更有趣的是:我怎样才能避免这样的问题?
I tried to avoid "intersects" by using other functions but the results were not helpful.我试图通过使用其他功能来避免“相交”,但结果没有帮助。 Please see calculations for b2 and b3.
请参阅 b2 和 b3 的计算。
PS: Unfortunately the example seems cause a crash on coliru. PS:不幸的是,这个例子似乎导致了 coliru 的崩溃。
In fact the return value of the intersection
function is unspecified: see实际上
intersection
function 的返回值是未指定的:见
What does boost::geometry::intersection return boost::geometry::intersection 返回什么
So, you need to look at the intersection itself:因此,您需要查看交叉点本身:
Live On Wandbox (Yay!)活在魔杖盒上(耶!)
#include <iostream>
#include <boost/geometry.hpp>
#include <boost/logic/tribool.hpp>
#include <boost/logic/tribool_io.hpp>
using boost::tribool;
using boost::indeterminate;
namespace bg = boost::geometry;
using Coord = double;
using point_t = bg::model::d2::point_xy<Coord>;
using polygon_t = bg::model::polygon<point_t>;
using mpolygon_t = bg::model::multi_polygon<polygon_t>;
int main() {
polygon_t a, b;
bg::read_wkt("POLYGON(("
"12227.0 4967.0000000000009, 12238.0 4967.0000000000009, "
"12238.0 4813.0000000000009, 12227.0 4813.0000000000009, "
"12227.0 4967.0000000000009))", a);
bg::read_wkt("POLYGON(("
"12254.0 4947.0, 12219.0 4982.0, 12219.0 5020.0, 12254.0 5055.0, "
"12261.0 5055.0, 12263.0 5055.0, 12283.0 5055.0, 12283.0 4947.0, "
"12263.0 4947.0, 12261.0 4947.0, 12254.0 4947.0))", b);
#define CHECK(expected, expr) \
do { \
auto const& actual = (expr); \
auto ok = ((expected) == actual); \
if (ok == true) { \
std::cout << "PASS"; \
} else if (ok == false) { \
std::cout << "FAIL"; \
} else { \
std::cout << "?"; \
} \
std::cout << "\t" << #expr << " -> " << std::boolalpha << actual \
<< "\n"; \
if (!(ok == true)) \
std::cout << " (expected value was " << (expected) << ")\n"; \
} while (false)
mpolygon_t ab_intersect;
auto dump = [](auto label, auto& geo) {
std::cout << label << " area " << bg::area(geo) << " " << bg::wkt(geo) << "\n";
};
CHECK(true, bg::intersection(a, b, ab_intersect));
CHECK(1, ab_intersect.size());
dump("a", a);
dump("b", b);
dump("ab_intersect", ab_intersect);
mpolygon_t a_minus_b, b_minus_a;
bg::difference(a, ab_intersect, a_minus_b);
bg::difference(b, ab_intersect, b_minus_a);
CHECK(1, a_minus_b.size());
CHECK(1, b_minus_a.size());
dump("a_minus_b", a_minus_b);
dump("b_minus_a", b_minus_a);
auto checks = [dump](auto& reduced, auto& other) {
CHECK(true, bg::intersects(reduced, other));
mpolygon_t check;
bg::intersection(reduced, other, check);
CHECK(true, check.empty());
dump("check", check);
};
std::cout << "-- reduced a vs b: -------\n";
checks(a_minus_b, b);
std::cout << "-- reduced b vs a: -------\n";
checks(b_minus_a, a);
}
Prints印刷
PASS bg::intersection(a, b, ab_intersect) -> true
PASS ab_intersect.size() -> 1
a area 1694 POLYGON((12227 4967,12238 4967,12238 4813,12227 4813,12227 4967))
b area 5687 POLYGON((12254 4947,12219 4982,12219 5020,12254 5055,12261 5055,12263 5055,12283 5055,12283 4947,12263 4947,12261 4947,12254 4947))
ab_intersect area 8 MULTIPOLYGON(((12234 4967,12238 4967,12238 4963,12234 4967)))
PASS a_minus_b.size() -> 1
PASS b_minus_a.size() -> 1
a_minus_b area 1686 MULTIPOLYGON(((12234 4967,12238 4963,12238 4813,12227 4813,12227 4967,12234 4967)))
b_minus_a area 5679 MULTIPOLYGON(((12238 4963,12238 4967,12234 4967,12219 4982,12219 5020,12254 5055,12261 5055,12263 5055,12283 5055,12283 4947,12263 4947,12261 4947,12254 4947,12238 4963)))
-- reduced a vs b: -------
PASS bg::intersects(reduced, other) -> true
PASS check.empty() -> true
check area 0 MULTIPOLYGON()
-- reduced b vs a: -------
PASS bg::intersects(reduced, other) -> true
PASS check.empty() -> true
check area 0 MULTIPOLYGON()
The behavior I mentioned is not a bug but fully correct:我提到的行为不是错误,而是完全正确的:
bg::intersection() returns an empty polygon BUT bg::intersection() 返回一个空多边形但是
if I call it with a linestring as output parameter:如果我用线串作为 output 参数调用它:
using linestring_t = bg::model::linestring<point_t>;
linestring_t int1;
bg::intersection(poly2, poly4, int1);
std::cout << "int1: " << bg::wkt(int1) << std::endl;
it works.有用。
TL;DR The usage and my interpretation of bg::intersects() and bg::intersection() was wrong! TL;DR bg::intersects() 和 bg::intersection() 的用法和我的解释是错误的!
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