bih_tree.cc

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/*!
 *
 * Copyright (C) 2015 Technical University of Liberec.  All rights reserved.
 * 
 * This program is free software; you can redistribute it and/or modify it under
 * the terms of the GNU General Public License version 3 as published by the
 * Free Software Foundation. (http://www.gnu.org/licenses/gpl-3.0.en.html)
 * 
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
 *
 * 
 * @file    bih_tree.cc
 * @brief   
 */

#include "mesh/bih_tree.hh"
#include "mesh/bih_node.hh"
#include "system/global_defs.h"
#include <ctime>
#include <stack>

/**
 * Minimum reduction of box size to allow
 * splitting of a node during tree creation.
 */
const double BIHTree::size_reduce_factor = 0.8;


BIHTree::BIHTree(Mesh* mesh, unsigned int soft_leaf_size_limit)
: mesh_(mesh), leaf_size_limit(soft_leaf_size_limit), r_gen(123)
{
    OLD_ASSERT(mesh != nullptr, " ");
    max_n_levels = 2*log(mesh->n_elements())/log(2);

    nodes_.reserve(2*mesh_->n_elements() / leaf_size_limit);
    element_boxes();

    in_leaves_.resize(elements_.size());
    for(unsigned int i=0; i<in_leaves_.size(); i++) in_leaves_[i] = i;

    // make root node
    nodes_.push_back(BIHNode());
    nodes_.back().set_leaf(0, in_leaves_.size(), 0, 0);
    // make root box
    Node* node = mesh_->node_vector.begin();
    main_box_ = BoundingBox(node->point(), node->point());
    FOR_NODES(mesh_, node ) {
        main_box_.expand( node->point() );
    }

    make_node(main_box_, 0);
}


BIHTree::~BIHTree() {

}


void BIHTree::split_node(const BoundingBox &node_box, unsigned int node_idx) {
    BIHNode &node = nodes_[node_idx];
    OLD_ASSERT(node.is_leaf(), " ");
    unsigned int axis = node_box.longest_axis();
    double median = estimate_median(axis, node);

    // split elements in node according to the median
    auto left = in_leaves_.begin() + node.leaf_begin(); // first of unresolved elements in @p in_leaves_
    auto right = in_leaves_.begin() + node.leaf_end()-1; // last of unresolved elements in @p in_leaves_

    double left_bound=node_box.min(axis); // max bound of the left group
    double right_bound=node_box.max(axis); // min bound of the right group

    while (left != right) {
        if  ( elements_[ *left ].projection_center(axis) < median) {
            left_bound = std::max( left_bound, elements_[ *left ].max(axis) );
            ++left;
        }
        else {
            while ( left != right
                    &&  elements_[ *right ].projection_center(axis) >= median ) {
                right_bound = std::min( right_bound, elements_[ *right ].min(axis) );
                --right;
            }
            std::swap( *left, *right);
        }
    }
    // in any case left==right is now the first element of the right group

    if ( elements_[ *left ].projection_center(axis) < median) {
        left_bound = std::max( left_bound, elements_[ *left ].max(axis) );
        ++left;
        ++right;
    } else {
        right_bound = std::min( right_bound, elements_[ *right ].min(axis) );
    }

    unsigned int left_begin = node.leaf_begin();
    unsigned int left_end = left - in_leaves_.begin();
    unsigned int right_end = node.leaf_end();
    unsigned int depth = node.depth()+1;
    // create new leaf nodes and possibly call split_node on them
    // can not use node reference anymore
    nodes_.push_back(BIHNode());
    nodes_.back().set_leaf(left_begin, left_end, left_bound, depth);
    nodes_.push_back(BIHNode());
    nodes_.back().set_leaf(left_end, right_end, right_bound, depth);

    nodes_[node_idx].set_non_leaf(nodes_.size()-2, nodes_.size()-1, axis);
}


void BIHTree::make_node(const BoundingBox &box, unsigned int node_idx) {
    // we must refer to the node by index to prevent seg. fault due to nodes_ reallocation

    split_node(box,node_idx);

    {
        BIHNode &node = nodes_[node_idx];
        BIHNode &child = nodes_[ node.child(0) ];
        BoundingBox node_box(box);
        node_box.set_max(node.axis(), child.bound() );
        if (    child.leaf_size() > leaf_size_limit
            &&  child.depth() < max_n_levels
            &&  ( node.axis() != node_box.longest_axis()
                  ||  node_box.size(node_box.longest_axis()) < box.size(node.axis())  * size_reduce_factor )
            )
        {
                make_node(node_box, node.child(0) );
        }
    }

    {
        BIHNode &node = nodes_[node_idx];
        BIHNode &child = nodes_[ node.child(1) ];
        BoundingBox node_box(box);
        node_box.set_min(node.axis(), child.bound() );
        if (    child.leaf_size() > leaf_size_limit
            &&  child.depth() < max_n_levels
            &&  ( node.axis() != node_box.longest_axis()
                  ||  node_box.size(node_box.longest_axis()) < box.size(node.axis())  * size_reduce_factor )
            )
        {
                make_node(node_box, node.child(1) );
        }
    }
}


double BIHTree::estimate_median(unsigned char axis, const BIHNode &node)
{
    unsigned int median_idx;
    unsigned int n_elements = node.leaf_size();

    if (n_elements > max_median_sample_size) {
        // random sample
        std::uniform_int_distribution<unsigned int> distribution(node.leaf_begin(), node.leaf_end()-1);
        coors_.resize(max_median_sample_size);
        for (unsigned int i=0; i<coors_.size(); i++) {
            median_idx = distribution(this->r_gen);

            coors_[i] = elements_[ in_leaves_[ median_idx ] ].projection_center(axis);
        }

    } else {
        // all elements
        coors_.resize(n_elements);
        for (unsigned int i=0; i<coors_.size(); i++) {
            median_idx = node.leaf_begin() + i;
            coors_[i] = elements_[ in_leaves_[ median_idx ] ].projection_center(axis);
        }

    }

    unsigned int median_position = (unsigned int)(coors_.size() / 2);
    std::nth_element(coors_.begin(), coors_.begin()+median_position, coors_.end());

    return coors_[median_position];
}


unsigned int BIHTree::get_element_count() {
    return elements_.size();
}


const BoundingBox &BIHTree::tree_box() const {
    return main_box_;
}


void BIHTree::find_bounding_box(const BoundingBox &box, std::vector<unsigned int> &result_list) const
{
    std::stack<unsigned int, std::vector<unsigned int> > node_stack;
    OLD_ASSERT_EQUAL(result_list.size() , 0);

    node_stack.push(0);
    while (! node_stack.empty()) {
        const BIHNode &node = nodes_[node_stack.top()];
        //DebugOut().fmt("node: {}\n", node_stack.top() );
        node_stack.pop();


        if (node.is_leaf()) {

            //START_TIMER("leaf");
            for (unsigned int i=node.leaf_begin(); i<node.leaf_end(); i++) {
                if (elements_[ in_leaves_[i] ].intersect(box)) {

                    result_list.push_back(in_leaves_[i]);
                }
            }
            //END_TIMER("leaf");
        } else {
            //START_TIMER("recursion");
            if ( ! box.projection_gt( node.axis(), nodes_[node.child(0)].bound() ) ) {
                // box intersects left group
                node_stack.push( node.child(0) );
            }
            if ( ! box.projection_lt( node.axis(), nodes_[node.child(1)].bound() ) ) {
                // box intersects right group
                node_stack.push( node.child(1) );
            }
            //END_TIMER("recursion");
        }
    }


#ifdef FLOW123D_DEBUG_ASSERTS
    // check uniqueness of element indexes
    std::vector<unsigned int> cpy(result_list);
    sort(cpy.begin(), cpy.end());
    std::vector<unsigned int>::iterator it = unique(cpy.begin(), cpy.end());
    OLD_ASSERT_EQUAL(cpy.size() , it - cpy.begin());
#endif
}


void BIHTree::find_point(const Space<3>::Point &point, std::vector<unsigned int> &result_list) const
{
    find_bounding_box(BoundingBox(point), result_list);
}


void BIHTree::element_boxes() {
    elements_.resize(mesh_->element.size());
    unsigned int i=0;
    FOR_ELEMENTS(mesh_, element) {
        elements_[i] = element->bounding_box();

        i++;
    }
}