CODEWITHSUNDEEP
c++geometryboost-geometry
H'H
H'H

Reputation: 1678

divide boost segment into N equal segments using boost geometry

I created a line segment using boost geometry model. I am wondering if there is a way in boost to divide the segment into N equal line segments.

Please do not consider this question as duplicated version of this. (EDIT) because is over-dated and I have already tried the answer provided for this question.

Upvotes: 1

Views: 803

Answers (2)

sehe
sehe

Reputation: 393084

The simplest thing that comes to mind:

Live On Coliru

#include <boost/geometry/geometry.hpp>
#include <boost/geometry/io/io.hpp>
#include <boost/geometry/arithmetic/arithmetic.hpp>
#include <boost/geometry/geometries/segment.hpp>
#include <boost/geometry/geometries/point_xy.hpp>
#include <boost/geometry/geometries/linestring.hpp>

#include <iostream>

template <typename Segment, typename Point = typename boost::geometry::point_type<Segment>::type>
auto split_into(unsigned N, Segment const& s) {
    using namespace boost::geometry;
    assert(N>1);

    auto step = s.second;
    subtract_point(step, s.first);
    divide_value(step, N-1);

    std::vector<Point> segments;
    std::generate_n(back_inserter(segments), N, [accu=s.first, step] () mutable { Point p = accu; return add_point(accu, step), p; });

    return model::linestring<Point> {segments.begin(), segments.end()};
}

using namespace boost::geometry;
using Point = model::d2::point_xy<double>;

int main() {
    model::segment<Point> const line { {1,3}, {11,33} };

    std::cout << wkt(line) << "\n";
    std::cout << wkt(split_into(5, line)) << "\n";
}

Prints

LINESTRING(1 3,11 33)
LINESTRING(1 3,3.5 10.5,6 18,8.5 25.5,11 33)

Fancy Range Version

One that might scale better for large N:

Live On Coliru

#include <boost/range/adaptors.hpp>
#include <boost/range/irange.hpp>

template <typename Segment, typename Point = typename boost::geometry::point_type<Segment>::type>
auto split_into(unsigned N, Segment const& s) {
    using namespace boost::geometry;
    using namespace boost::adaptors;
    assert(N>1);

    auto step = s.second;
    subtract_point(step, s.first);
    divide_value(step, N-1);

    auto gen = boost::irange(0u, N) | transformed([=](int i) { auto p = step; multiply_value(p, i); add_point(p, s.first); return p; });
    return model::linestring<Point> { boost::begin(gen), boost::end(gen) };
}

Prints

LINESTRING(1 3,11 33)
LINESTRING(1 3,3.5 10.5,6 18,8.5 25.5,11 33)

Upvotes: 1

MBo
MBo

Reputation: 80187

If you need to divide AB segment to N equal pieces, then coordinates of starting point for i-th segment (and the end of previous segment) might be calculated using parametric equation of line.
Pseudocode:

for i = 0.. N-1
   t = i / N
   Start[i].X = A.X * (1 - t) + B.X * t
   Start[i].Y = A.Y * (1 - t) + B.Y * t

Upvotes: 0

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