random_points.cpp

//
// Created by RainSure on 2023/11/3.
//
 
#include "point_cloud/random_points.h"
 
#include <cmath>
#include <stdexcept>
 
#include "common/eigen_utility.h"
 
namespace rsmesh {
    namespace point_cloud {
        geometry::points3d random_points(const geometry::cuboid3d& cuboid,
                                         index_t n,
                                         seed_type seed) {
            auto size = cuboid.max() - cuboid.min();
            if (size.minCoeff() <= 0.0)
                throw std::invalid_argument("cuboid must have a positive volume.");
 
            std::mt19937 gen(seed);
            std::uniform_real_distribution<> dist(0.0, 1.0);
 
            geometry::points3d points(n, 3);
 
            for (auto p : common::row_range(points)) {
                auto x = dist(gen) * size(0);
                auto y = dist(gen) * size(1);
                auto z = dist(gen) * size(2);
 
                p = cuboid.min() + geometry::vector3d(x, y, z);
            }
 
            return points;
        }
 
        // See Marsaglia (1972) at:
        // http://mathworld.wolfram.com/SpherePointPicking.html
        geometry::points3d random_points(const geometry::sphere3d& sphere,
                                         index_t n,
                                         seed_type seed) {
            if (sphere.radius() <= 0.0)
                throw std::invalid_argument("sphere must have a positive volume.");
 
            std::mt19937 gen(seed);
            std::uniform_real_distribution<> dist(-1.0, 1.0);
 
            geometry::points3d points(n, 3);
 
            for (auto p : common::row_range(points)) {
                double x1;
                double x2;
                double rsq;
                do {
                    x1 = dist(gen);
                    x2 = dist(gen);
                    rsq = x1 * x1 + x2 * x2;
                } while (rsq >= 1.0);
 
                auto x = 2.0 * x1 * std::sqrt(1.0 - rsq);
                auto y = 2.0 * x2 * std::sqrt(1.0 - rsq);
                auto z = 1.0 - 2.0 * rsq;
 
                p = sphere.center() + sphere.radius() * geometry::vector3d(x, y, z);
            }
 
            return points;
        }
 
    } // rsmesh
} // point_cloud