Code: Select all

  ParametrizedLine<double, 2> line1;
  Hyperplane<double, 2> line2;
  line1 = ParametrizedLine<double, 2>::Through(Vector2d(-1,0), Vector2d(-0.5,0.0));
  line2 = Hyperplane<double, 2>::Through(Vector2d(0,1), Vector2d(0,-1));

  double inter = line1.intersection(line2);
  cout<<"inter: "<<inter<<endl;


the print there is printing 1 for me. exactly 1.
I was expecting some thing either greater than 1 or less than 0, since those lines don't intersect.
I'm using eigen 2.0.10 with gcc 4.3.4

thanks.

line1 is horizontal, line2 is vertical, so they do intersect. "Through" means that you're defining a line by giving 2 points through which it passes.

Ok, so I made some progress, but I just want to make sure I understand what's going on...

Code: Select all

  ParametrizedLine<double, 2> line1(Vector2d(-1.0,0.0), Vector2d(0.5,0.0));
  Hyperplane<double, 2> line2;
  line2 = Hyperplane<double, 2>::Through(Vector2d(0.0,1.0), Vector2d(0.0,-1.0));

  double inter = line1.intersection(line2);
  cout<<"inter: "<<inter<<endl;


that is the same code as before, but this time instead of using the "Through" function to create the ParameterizedLine I used the origin and direction constructor. the output from that code is 2, which makes sense to me because -1+2*0.5 = 0.
Here is what I don't get: the line1 variable in both the bit of code I posted represent the same line, so why is the result of the intersection different? Is it because I didn't specify a direction in the first one that it only returns 1 to say "they do intersect at some point". If so I find it very confusing, if the user passes in a line with created with Through then the code in a library may expect a line with a specific direction and length so the intersection function works a certain way.

Ok so now you are using the ParametrizedLine constructor taking a point and a direction vector. But that constructor assumes the direction vector to be normalized, as is explained in the documentation,
http://eigen.tuxfamily.org/dox/classEig ... 19ea17074f

So your first line is faulty, as (-0.5,0) is not a normalized vector.

I don't understand the rest of your questions. ParametrizedLine is a class representing a parametrized line, that is the data of a origin point and a direction unit vector. It offers a static method Through() constructing such a ParametrizedLine from the data of two points through which the line must pass. But that is still the same ParametrizedLine type.

ok, I missed the part about the normalization. intersection tests are as expected now.

thank you.