Question

i want to compute intersection line, given by 2 planes. my main program gives me, plane parameters a,b,-1,d (my equation is ax+by-z+d=0). so, my function for computing equation of intersection line is as;

vector<double> LineofIntersection(vector<double> plane1,vector<double> plane2) {
     double a1=plane1.at(0);    double a2=plane2.at(0);
     double b1=plane1.at(1);    double b2=plane2.at(1);
     double d1=plane1.at(2);    double d2=plane2.at(2);
     int c1=-1,c2=-1;
     double cros_x=fabs((b1*c2)-(b2*c1));
     double cros_y=fabs((a2*c1)-(a1*c2));
     double cros_z=fabs((a1*b2)-(a2*b1));
     vector <double> point; vector <double> pointout;

     int maxc;   // max coordinate
     if (cros_x > cros_y){
        if (cros_x > cros_z)
             maxc = 1;
        else maxc = 3;
        }
     else {
        if (cros_y > cros_z)
             maxc = 2;
        else maxc = 3;
        }
     //
     vector <double> point; vector <double> pointout;
     switch (maxc) {  // select max coordinate          
     case 1: // intersect with x=0                   
        point.at(0)=0;
        point.at(1)=(d2-d1)/(b2-b1);
        point.at(2)=(b1*d2-2*b1*d1+d1*b2)/(b2-b1);
        break;
     case 2: // intersect with y=0                   
        point.at(0)=(d2-d1)/(a1-a2);
        point.at(1)=0;
        point.at(2)=(a1*d2-a2*d1)/(a1-a2);
        break;
     case 3: // intersect with z=0                   
        point.at(0)=(b1*d2-b2*d1)/(a1*b2-a2*b1);
        point.at(1)=(a2*d1-a1*d2)/(a1*b2-a2*b1);
        point.at(2)=0;
        break;
     }   
     pointout.push_back(point.at(0));
     pointout.push_back(point.at(1));
     pointout.push_back(point.at(2));
     return pointout;
}

in the main program, i call this function as:

vector<double> linep=LineofIntersection(plane1,plane2);
cout<<linep.at(1)<<" "<<linep.at(1)<<" "<<linep.at(2);

but, i got error message and cannot run the program. any help please.

Answer 1

Fundementally, your problem is that you are assigning to locations in the point vector without first allocating them. Additionally, pointout serves no purpose, and you have a syntax error. Here are my recommendations:

 vector <double> point; vector <double> pointout;

This line appears twice. Delete the line the first time it appears, and replace the second instance with:

vector <double> point(3);

Notice the (3). Without it, point is an empty vector, i.e. it has no doubles in it at all. With it, it has 3 doubles.

The pointout object serves no purpose. Replace these two lines:

pointout.push_back(point.at(0));pointout.push_back(point.at(1));pointout.push_back(point.at(2));
return pointout;

with this line:

return point;