double estimate_volume(const mesh& mesh) {
const auto& nodes = mesh.get_structure().get_condensed_nodes();
const auto num_inside =
std::count_if(cbegin(nodes), cend(nodes), [](const auto& i) {
return is_inside(i);
});
const auto spacing = mesh.get_descriptor().spacing;
const auto node_volume = spacing * spacing * spacing;
return node_volume * num_inside;
}
bool is_inside(const mesh& m, size_t node_index) {
return is_inside(m.get_structure().get_condensed_nodes()[node_index]);
}