[英]boost geometry polygon distance for inside point
我正在使用boost::geometry
處理一些幾何任務。 我需要滿足兩個要求:
boost::geometry::within
一起使用效果很好,那就很好 boost::geometry::distance
正確處理多邊形外部的點,但是似乎將多邊形視為實體。 因此,多邊形內的每個點到多邊形的距離顯然為0。 我嘗試對內部/外部內容進行實驗,想知道是否有可能獲取多邊形的內部和外部點的距離。
如果點在多邊形內部,則可以使用comparable_distance
而不是distance
算法來加快代碼的速度。 您無需為每個分段點對計算確切的距離。 使用查找多邊形到指定點最近的段comparable_distance
,然后用計算的實際距離distance
算法。
auto distance = std::numeric_limits<float>::max();
if(boost::geometry::within(pt, mPolygon))
{
Segment nearestSegment;
boost::geometry::for_each_segment(mPolygon,
[&distance, &pt, &nearestSegment](const auto& segment)
{
double cmpDst = boost::geometry::comparable_distance(segment,pt);
if (cmpDst < distance)
{
distance = cmpDst;
nearestSegment = segment; // UPDATE NEAREST SEGMENT
}
});
// CALCULATE EXACT DST
distance = boost::geometry::distance(nearestSegment,pt);
} else {
distance = boost::geometry::distance(pt, mPolygon);
}
我決定使用以下方法,到目前為止似乎可以提供正確的結果:
const TPolygonPoint pt{ x, y };
auto distance = std::numeric_limits<float>::max();
if(boost::geometry::within(pt, mPolygon)) {
boost::geometry::for_each_segment(mPolygon, [&distance, &pt](const auto& segment) {
distance = std::min<float>(distance, boost::geometry::distance(segment, pt));
});
} else {
distance = boost::geometry::distance(pt, mPolygon);
}
return distance;
如果有人知道更快或更更好的方法,請發表評論:)
為了獲得最佳性能,您應該使用帶有boost :: geometry :: index的RTree。 創建RTree需要付出一定的代價,但是計算到任何(多)多邊形環的點的距離將非常快。 示例代碼:
#include <boost/geometry.hpp>
#include <boost/geometry/geometries/geometries.hpp>
#include <boost/geometry/index/rtree.hpp>
#include <iostream>
#include <vector>
int main()
{
namespace bg = boost::geometry;
namespace bgi = boost::geometry::index;
typedef bg::model::point<double, 2, bg::cs::cartesian> point;
typedef bg::model::polygon<point> polygon;
point p{ 0, 0 };
// create some polygon and fill it with data
polygon poly;
double a = 0;
double as = bg::math::two_pi<double>() / 100;
for (int i = 0; i < 100; ++i, a += as)
{
double c = cos(a);
double s = sin(a);
poly.outer().push_back(point{10 * c, 10 * s});
poly.inners().resize(1);
poly.inners()[0].push_back(point{5 * c, 5 * s});
}
// make sure it is valid
bg::correct(poly);
// create rtree containing objects of type bg::model::pointing_segment
typedef bg::segment_iterator<polygon const> segment_iterator;
typedef std::iterator_traits<segment_iterator>::value_type segment_type;
bgi::rtree<segment_type, bgi::rstar<4> > rtree(bg::segments_begin(poly),
bg::segments_end(poly));
// get 1 nearest segment
std::vector<segment_type> result;
rtree.query(bgi::nearest(p, 1), std::back_inserter(result));
BOOST_ASSERT(!result.empty());
std::cout << bg::wkt(result[0]) << ", " << bg::distance(p, result[0]) << std::endl;
return 0;
}
如果您向與外邊界重合的多邊形添加內邊界[ Polygon Concept ],則可以直接使用boost :: geometry :: distance。
#include <iostream>
#include <boost/geometry.hpp>
#include <boost/geometry/geometries/geometries.hpp>
namespace bg = boost::geometry;
int main() {
typedef bg::model::point<int, 2, bg::cs::cartesian> point_t;
typedef bg::model::polygon<point_t> polygon_t;
polygon_t poly1;
bg::append (poly1.outer(), point_t (1, -1));
bg::append (poly1.outer(), point_t (1, 1));
bg::append (poly1.outer(), point_t (-1, 1));
bg::append (poly1.outer(), point_t (-1, -1));
bg::append (poly1.outer(), point_t (1, -1));
poly1.inners().resize (1);
bg::append (poly1.inners()[0], point_t (1, -1));
bg::append (poly1.inners()[0], point_t (1, 1));
bg::append (poly1.inners()[0], point_t (-1, 1));
bg::append (poly1.inners()[0], point_t (-1, -1));
bg::append (poly1.inners()[0], point_t (1, -1));
point_t myPoint (0, 0);
std::cout << "Minimal distance: " << bg::distance (poly1, myPoint) << std::endl;
std::cout << "Is within: " << bg::within (myPoint, poly1) << std::endl;
return 0;
}
->將返回:
Minimal distance: 1
Is within: 0
但是,如果執行此操作,則通過boost :: geometry :: within將嚴格限制在多邊形內部的點視為在多邊形“外部”。 如果需要這兩種功能,則可以維護兩個單獨的多邊形-一個具有內部邊界,另一個不具有內部邊界。
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