【发布时间】：2017-09-28 20:30:55
【问题描述】：
在使用 Fade 库的 Delaunay 三角剖分中，可以访问事件三角形到站点并访问其邻居，如下所述：http://www.geom.at/example2-traversing/
我不知道如何通过利用事件三角形及其邻居来遍历站点邻居站点。我应该在每次迭代中访问哪个三角形邻居来完成这个？
在下面的示例中，主站点位于蓝色圆圈中，我想将红色圆圈中的所有相邻站点保存在某个数组中。 .
【问题讨论】：
【发布时间】：2017-09-28 20:30:55
【问题描述】：
这段代码为this example 提供了正确的输出，但我认为这不是一种有效的方法。我相信对于大量网站来说这会很慢。
#include <stdio.h>
#include <iostream>
#include <Fade_2D.h>
using namespace GEOM_FADE2D;
using namespace std;
const int NUM_EXAMPLES(7);
// Defined in the exampleX files
int main()
{
int pointToCheck;
bool incidentResetted;
cout << endl;
std::vector<Point2> vInputPoints;
// Create a triangulation
Fade_2D dt;
// Create and insert 4 points
Point2 p1(8.3, 1);
Point2 p2(7.6, 8);
Point2 p3(7.4, 7);
Point2 p4(3.9, 3);
Point2 p5(6.5, 9.5);
Point2 p6(1.7, 0.4);
Point2 p7(7, 4.2);
Point2 p8(0.3, 3.9);
Point2 p9(2.8, 7.7);
Point2 p10(0.4, 8);
p1.setCustomIndex(1);
p2.setCustomIndex(2);
p3.setCustomIndex(3);
p4.setCustomIndex(4);
p5.setCustomIndex(5);
p6.setCustomIndex(6);
p7.setCustomIndex(7);
p8.setCustomIndex(8);
p9.setCustomIndex(9);
p10.setCustomIndex(10);
vInputPoints.push_back(p1);
vInputPoints.push_back(p2);
vInputPoints.push_back(p3);
vInputPoints.push_back(p4);
vInputPoints.push_back(p5);
vInputPoints.push_back(p6);
vInputPoints.push_back(p7);
vInputPoints.push_back(p8);
vInputPoints.push_back(p9);
vInputPoints.push_back(p10);
std::vector<Point2*> vDelaunayVertexPointers;
dt.insert(vInputPoints, vDelaunayVertexPointers);
//Draw
dt.show("example.ps");
std::vector<Point2*> vAllPoints;
vAllPoints.clear();
dt.getVertexPointers(vAllPoints);
while (true)
{
cout << "Please enter point to check: ";
cin >> pointToCheck;
for (std::vector<Point2*>::iterator it(vAllPoints.begin());
it != vAllPoints.end(); ++it)
{
Point2* currentPoint(*it);
incidentResetted = false;
vector<Point2*> neighbours;
if (currentPoint->getCustomIndex() == pointToCheck)
{
//Print neighbours
Triangle2* pT(currentPoint->getIncidentTriangle());
Triangle2* firstTr(currentPoint->getIncidentTriangle());
Triangle2* lastcheckedTriangle;
lastcheckedTriangle = pT;
timer("INSERT"); // Start timer
if (pT->getCorner(0)->getCustomIndex() == currentPoint->getCustomIndex())
{
neighbours.push_back(pT->getCorner(1));
neighbours.push_back(pT->getCorner(2));
if (pT->getOppositeTriangle(1) != NULL)
pT = pT->getOppositeTriangle(1);
else
pT = pT->getOppositeTriangle(2);
}
else if (pT->getCorner(1)->getCustomIndex() == currentPoint->getCustomIndex())
{
neighbours.push_back(pT->getCorner(0));
neighbours.push_back(pT->getCorner(2));
if (pT->getOppositeTriangle(0) != NULL)
pT = pT->getOppositeTriangle(0);
else
pT = pT->getOppositeTriangle(2);
}
else if (pT->getCorner(2)->getCustomIndex() == currentPoint->getCustomIndex())
{
neighbours.push_back(pT->getCorner(0));
neighbours.push_back(pT->getCorner(1));
if (pT->getOppositeTriangle(0) != NULL)
pT = pT->getOppositeTriangle(0);
else
pT = pT->getOppositeTriangle(1);
}
if ( pT == NULL)
break;
while (pT != firstTr)
{
if (pT->getCorner(0)->getCustomIndex() == currentPoint->getCustomIndex())
{
if (pT->getCorner(1)->getCustomIndex() != neighbours.back()->getCustomIndex())
{
neighbours.push_back(pT->getCorner(1));
}
else
{
neighbours.push_back(pT->getCorner(2));
}
if (pT->getOppositeTriangle(1) != lastcheckedTriangle)
{
lastcheckedTriangle = pT;
pT = pT->getOppositeTriangle(1);
}
else
{
lastcheckedTriangle = pT;
pT = pT->getOppositeTriangle(2);
}
}
else if (pT->getCorner(1)->getCustomIndex() == currentPoint->getCustomIndex())
{
if (pT->getCorner(0)->getCustomIndex() != neighbours.back()->getCustomIndex())
{
neighbours.push_back(pT->getCorner(0));
}
else
{
neighbours.push_back(pT->getCorner(2));
}
if (pT->getOppositeTriangle(0) != lastcheckedTriangle)
{
lastcheckedTriangle = pT;
pT = pT->getOppositeTriangle(0);
}
else
{
lastcheckedTriangle = pT;
pT = pT->getOppositeTriangle(2);
}
}
else if (pT->getCorner(2)->getCustomIndex() == currentPoint->getCustomIndex())
{
if (pT->getCorner(1)->getCustomIndex() != neighbours.back()->getCustomIndex())
{
neighbours.push_back(pT->getCorner(1));
}
else
{
neighbours.push_back(pT->getCorner(0));
}
if (pT->getOppositeTriangle(1) != lastcheckedTriangle)
{
lastcheckedTriangle = pT;
pT = pT->getOppositeTriangle(1);
}
else
{
lastcheckedTriangle = pT;
pT = pT->getOppositeTriangle(0);
}
}
else
{
break;
}
//checking a case in which the currectPoint is on the boundary and the incident triangle is some in between triangle
if (pT == NULL)
{
if (incidentResetted)
break;
else
{
incidentResetted = true;
//Need to reset everything and start again from this triangle
neighbours.clear();
currentPoint->setIncidentTriangle(lastcheckedTriangle);
pT = lastcheckedTriangle;
firstTr = pT;
if (pT->getCorner(0)->getCustomIndex() == currentPoint->getCustomIndex())
{
neighbours.push_back(pT->getCorner(1));
neighbours.push_back(pT->getCorner(2));
if (pT->getOppositeTriangle(1) != NULL)
pT = pT->getOppositeTriangle(1);
else
pT = pT->getOppositeTriangle(2);
}
else if (pT->getCorner(1)->getCustomIndex() == currentPoint->getCustomIndex())
{
neighbours.push_back(pT->getCorner(0));
neighbours.push_back(pT->getCorner(2));
if (pT->getOppositeTriangle(0) != NULL)
pT = pT->getOppositeTriangle(0);
else
pT = pT->getOppositeTriangle(2);
}
else if (pT->getCorner(2)->getCustomIndex() == currentPoint->getCustomIndex())
{
neighbours.push_back(pT->getCorner(0));
neighbours.push_back(pT->getCorner(1));
if (pT->getOppositeTriangle(0) != NULL)
pT = pT->getOppositeTriangle(0);
else
pT = pT->getOppositeTriangle(1);
}
}
}
}
timer("INSERT"); // End timer
if (neighbours.front()->getCustomIndex() == neighbours.back()->getCustomIndex())
neighbours.pop_back();
cout << "Neighbour sites:\n";
for (int l = 0; l < neighbours.size(); l++)
{
cout << neighbours[l]->getCustomIndex() << " | " << neighbours[l]->x() << " , " << neighbours[l]->y() << endl;
}
cout << "\n\n\n";
}
//dt.remove(currentPoint);
}
}
return 0;
}
【讨论】：
-
这是一个迟到的答案，抱歉：您不必遍历 vAllPoints 来查找 $currentPoint 因为 vDelaunayVertexPointers 中的顶点指针和 vInputPoints 中的输入点具有相同的顺序。让自定义索引从 0 开始。然后您可以使用 vDelaunayVertexPointers[pointToCheck] 在 O(1) 时间内快速找到 $currentPoint。此外，使用 TriangleAroundVertexIterator 更容易，并且可以避免大部分代码行。
我是 Fade2D 的作者。使用 TriangleAroundVertexIterator 或 Fade_2D::getIncidentTriangles() 方法会容易得多，请参见下面的演示函数：它创建一个随机三角剖分，为某个点提取周围的顶点并绘制结果：
vector<Point2> vRandomPoints;
generateRandomPoints(50,0,1000,vRandomPoints,1);
Fade_2D dt;
vector<Point2*> vVertexHandles;
dt.insert(vRandomPoints,vVertexHandles);
// Your point index to be checked and the corresponding pointer
size_t pointToCheck=5;
Point2* pVertexToCheck(vVertexHandles[pointToCheck]);
// Fetch the incident triangles
std::vector<Triangle2*> vIncidentTriangles;
dt.getIncidentTriangles(pVertexToCheck,vIncidentTriangles);
// Extract the vertices
set<Point2*> sResultVertices;
for(std::vector<Triangle2*>::iterator it(vIncidentTriangles.begin());
it!=vIncidentTriangles.end();++it)
{
Triangle2* pIncidentT(*it);
int intraTriangleIndex(pIncidentT->getIntraTriangleIndex(pVertexToCheck));
sResultVertices.insert(pIncidentT->getCorner((intraTriangleIndex+1)%3));
sResultVertices.insert(pIncidentT->getCorner((intraTriangleIndex+2)%3));
}
cout<<"number of points: "<<sResultVertices.size()<<endl;
// Verify: Postscript Visualization
Visualizer2 vis("result.ps");
dt.show(&vis,false);
vis.addObject(Label(*pVertexToCheck,"base"),Color(CGREEN));
for(set<Point2*>::iterator it(sResultVertices.begin());it!=sResultVertices.end();++it)
{
vis.addObject(Label(**it,"VTX"),Color(CRED));
}
vis.writeFile();
【讨论】：
-
非常感谢您的回答。我收到此错误：找不到“incIndexBy1”标识符。你能帮我解决吗？
-
对不起：incIndexBy1(idx) 是我环境中的一个小帮手。当使用 idx 调用时，它返回 (idx+1)%3，因此 incIndexBy1(0)=1、incIndexBy1(1)=2 和 incIndexBy1(2)=0。
-
谢谢！我刚刚注意到，如果该点是边缘点，则会错过第一个邻居：ibb.co/ih5n0Q
-
是的，演示代码假定了一个内部顶点。我现在已经编辑了代码，它现在也适用于边界顶点。