What must done for knowing on which node camera moves?

[r3i]

I want to give to some paths names and I want check if the camera is walking on these paths with collision detection... I've tried with a ray from camera to the ground but it' doesn't work...maybe I've made some misktakes!!
My code:

line3d<f32> line;

line.start = telecameraRegistrata->getPosition();
line.end = line.start - vector3df(0,2,0 );
electedSceneNode = gestoreCollisione->getSceneNodeFromRayBB(line,id );