#include <iostream>
#include <list>
#include <fstream>
#include <string>
#include <sstream>
#include <vector>
#include <iomanip>
#include <cmath>
using namespace std;

struct vector3D{
double x;
double y;
double z;
};

/**
* print v3d to screen using its 2d coordiante
*/
void worldToScreen(vector3D & v3d){
cout << setw(10) << v3d.x << " " << setw(10) << v3d.y << "\n";
}

int readFile(string file_name, list<string> & a_list){
// make a stream to read the file
fstream in;
// open the file
in.open(file_name, ios::in);

// check the state of the stream
if (in.is_open() == false) {
   return 0;
}

// declare a string and a list
string line;

// read each line of the file until reaching to the end of file
while (getline(in, line, '\n')) {
   /// push the line to the end of the list
   a_list.push_back(line);
}
// close the input stream
in.close();
return 1;
}

void listToFaces(list<string> & a_list, list<vector<vector3D>> & faces){
faces.clear();
string line;
vector3D v3d;
vector<vector3D> vt;

// iterate over the list
// print each line out
for (list<string>::iterator it = a_list.begin(); it != a_list.end(); it++) {
   // get a line from vector of lines
   // it is iterator or a pointer to a string which is a line in thiscase
   // *it is the value pointed by the pointer (iterator)
   // so it it the string "line" we are expecting for
   line = *it;

   // the line which contains "J" always has length of 1
   // there isn't any vector
   if (line.length() <= 1) {
         //cout << line << "\n";
         if (vt.empty() == false) {
            faces.push_back(vt);
            vt.clear();
         }

Compare and contrast use of extrusion node, ElevationGrid node and...