Example using TTL and the half-edge data structure

// File: main.cpp
// Created:
// Author: Řyvind Hjelle <oyvind.hjelle@math.sintef.no>
// Revision: $Id: main.cpp,v 1.2 2006/07/26 12:08:44 oyvindhj Exp $
// Description:
// Copyright (C) 2000-2003 SINTEF Applied Mathematics.  All rights reserved.
// This file is part of an example program for TTL.  This example
// program may be used, distributed and modified without limitation.


#include <ttl/halfedge/HeTriang.h>
#include <ttl/halfedge/HeDart.h>
#include <ttl/halfedge/HeTraits.h>
//using namespace hed; // (to avoid using prefix hed::)

#include <fstream>
#include <iostream>
#include <algorithm>
using namespace std;

// ------------------------------------------------------------------------------------------------
// Interpret two points as being coincident
inline bool eqPoints(hed::Node*& p1, hed::Node*& p2) {
  double dx = p1->x() - p2->x();
  double dy = p1->y() - p2->y();
  double dist2 = dx*dx + dy*dy;
  const double eps = 1.0e-12;
  if (dist2 < eps)
    return true;
  return false;

// ------------------------------------------------------------------------------------------------
// Lexicographically compare two points (2D)
inline bool ltLexPoint(const hed::Node* p1, const hed::Node* p2) {  
  return (p1->x() < p2->x()) || (p1->x() == p2->x() && p1->y() < p2->y());

// =================================================================================================
// A main program using TTL and the half-edge data structure to create
// a Delaunay triangulation.
// The program also demonstrates how to use other function templates in TTL.
// =================================================================================================

int main() {
  // ===============================================================
  // ===============================================================
  // Create random test data.
  int no_of_nodes = 100;
  std::vector<hed::Node*>* nodes = ttl_util::createRandomData<hed::Node>(no_of_nodes);

  // Sort the nodes lexicographically in the plane.
  // This is recommended since the triangulation algorithm will run much faster.
  // (ltLexPoint is defined above)
  std::sort(nodes->begin(), nodes->end(), ltLexPoint);
  // Remove coincident points to avoid degenerate triangles. (eqPoints is defined above)
  std::vector<hed::Node*>::iterator new_end = std::unique(nodes->begin(), nodes->end(), eqPoints);
  // Make the triangulation
  hed::Triangulation triang;
  triang.createDelaunay(nodes->begin(), new_end);
  // <... Print triangulation; see end of file ...>
  // ========================================================
  // SOME EXAMPLES USING TTL (Functions in namespace ttl)
  // ========================================================
  // Insert a new node in the Delaunay triangulation.
  // We need an arbitrary CCW (counterclockwise) dart for TTL.
  // Make the dart from the first edge in the list of leading edges.
  // ( Could also use Triangulation::createDart() )
  const list<hed::Edge*>& l_edges = triang.getLeadingEdges();
  hed::Edge* edge = *l_edges.begin();
  hed::Dart dart(edge);
  hed::Node* point = new hed::Node(0.3, 0.6, 0);
  ttl::insertNode<hed::TTLtraits>(dart, *point);
  // Locate a triangle in the triangulation containing the given point.
  // The given dart will be repositioned to that triangle while maintaining
  // its orientation (CCW or CW).
  // If the given point is outside the triangulation, the dart will be
  // positioned at a boundary edge.
  point->init(0.5, 0.5, 0);
  bool found = ttl::locateTriangle<hed::TTLtraits>(*point, dart);
  if (!found) {
    cout << "The given points is outside the triangulation" << endl;
    // (and the dart is positioned at a boundary edge)
  // The degree (or valency) of a node V in a triangulation, is defined
  // as the number of edges incident with V.
  // Get the degree of the node associated with the dart.
  int degree = ttl::getDegreeOfNode(dart);
  cout << "Degree of node = " << degree << endl;

  // Check if the edge associated with the dart is at the boundary of the triangulation.
  if (ttl::isBoundaryEdge(dart))
    cout << "The edge is at the boundary" << endl;

  // Check if the node associated with the dart is at the boundary of the triangulation.
  if (ttl::isBoundaryNode(dart))
    cout << "The node is at the boundary" << endl;

  // Remove the node associated with the dart used above.
  // Get the boundary of the triangulation represented as a list of darts.
  // Start with an arbitrary dart at the boundary.
  edge = triang.getBoundaryEdge();
  hed::Dart b_dart(edge);
  list<hed::Dart> boundary;
  cout << "No. of edges on boundary = " << boundary.size() << endl;

  // Check if the triangulation is Delaunay
  // (This is not a TTL function)
  if (triang.checkDelaunay())    
    cout << "Triangulation is Delaunay" << endl;
    cout << "WARNING: Triangulation is not Delaunay" << endl;

  // Insert two nodes and then insert a constrained edge between them
  // (Note that this could also be implemented in the code for the data structure.
  //  Here we call ttl directly to demonstrate the generic concept.) 
  hed::Dart d1 = triang.createDart(); // an arbitrary CCW dart
  ttl::insertNode<hed::TTLtraits>(d1, *new hed::Node(0.1, 0.25, 0));
  hed::Dart d2 = triang.createDart();
  ttl::insertNode<hed::TTLtraits>(d2, *new hed::Node(0.6, 0.85, 0));
  // (Note that d1 is not necessarily valid after having inserted d2 since insertion
  //  of d2 may affect d1. Here d2 is "far from" d1, so we are relatively safe).
  bool optimizeDelaunay = true; // optimizes to a constrained Delaunay triangulation
  dart = ttl::insertConstraint<hed::TTLtraits>(d1, d2, optimizeDelaunay);

  // Set the edge as constrained (fixed) such that it is not swapped when inserting nodes later

  // Insert nodes and a constraint near that above to demonstrate fixed edges
  d1 = triang.createDart();
  ttl::insertNode<hed::TTLtraits>(d1, *new hed::Node(0.35, 0.56, 0));
  d2 = triang.createDart();
  ttl::insertNode<hed::TTLtraits>(d2, *new hed::Node(0.1, 0.9, 0));
  dart = ttl::insertConstraint<hed::TTLtraits>(d1, d2, optimizeDelaunay);

  // Check if the boundary is convex (in the plane)
  if (ttl::convexBoundary<hed::TTLtraits>(b_dart))
    cout << "\nBoundary is convex:" << endl;

  // Print the nodes at the boundary
  list<hed::Dart>::const_iterator it;
  for (it = boundary.begin();  it != boundary.end(); ++it)
    cout << it->getNode()->x() << " " << it->getNode()->y() << '\n';
  // Print the triangulation (its edges)  to file
  // (for gnuplot or other line drawing programs)
  cout << "\nPrinting edges to file qweEdges.dat..." << endl;
  cout << "Plot triangulation with: gnuplot qwe.gnu" << endl;

  ofstream ofile("qweEdges.dat");
  return 0;

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