I read those tutorials but they do not say much about vectors.
My recommendation was not limited to vectors but to general stuff. Your code and your answers show that you're missing important basic knowledge.
There are many vector commands in the manual which could be helpful for this task but tutorials about them are rare.
Vector tutorials do not make much sense because they are a tools to achieve things, like bricks for a bricklayer. Now, a tutorial about bricks wouldn't help a brickalyer much, would it? He has to learn about bricks while learning how to lay bricks.
I think that vec_for_screen or vec_to_screen could be usefull for this task.
You're right about this.
And PLEASE: indent your code and use code tags as Kartoffel already told you.
