Layers on z axis

Im writing software for 3D printer, for something like this. []( My software open STL files and show 3D model, and this is all i have for now. Problem is that software must cut this model on rasters , layers, and calculate vector for all conturs and this is what i cant do , im wondering witch procedures should i use for this , meybe some of you can sugest some methods for this, im begginer in opengl so it is little hard for me to find good method for me.

It is pretty simple. It just involves linear interpolation between 2 vertices in a triangle and you get a new point in between them. No need to think of contours. No need for GL either.
You would do that for all triangles and you get yourself a contour made of all those points on the z axis. Connecting them gives you a contour.

I think i understand what u want to say but, how to calculate this (linear interpolation) . for example if model is a ball im cutting it by glClipPlane(GL_CLIP_PLANE0, @Plane); , but this is not my layer only a (for example half of a ball) but i need layer im wondering is my method ok for for this. so v-man can u write something more about calulating this linear interpolation.
from witch triangles i schold calculate this , becouse i think i cant calculate vertices on other sites of model).

I was thinking about it and now i know that my last post dos not have any sens. so i will ask is there any function in opengl to caltulate point between 2 points on z axis ? or i have to caltulate it by my own?
2. if i will have my points , how i will be know how to connect them (witch point witch with point).