How to select an edge?

[PengSi]

If a model is loaded in the scene, how to select an edge of the model with the mouse?

[rickertm]

If you are looking to integrate this into a user interface based on the Coin3D scene graph, you can use the SoRayPickAction class for this. The documentation of the class includes a small example on how to implement this.

For the collision detection engines in rl::sg, the class rl::sg::RaycastScene provides an abstraction to retrieve the shape in the scene hit by a 3D ray.