How to get the normals of a mesh with material nodes

Hi there,
the title says everything : how is it possible to obtain the normals of a mesh in the material nodes editor ?
I know there is a “geometry>>normal” node, but the problem with it is that it returns the normals in “camera space”, so to say… Which can be useful sometimes (for Fresnel effects for instance), but sometimes not. In my case, I would like to be able to obtain the “slope” value for each face of a mesh : does the face point toward the sky, or not ? And this is not possible with the normals in camera space (the vectors move when the camera moves… :frowning: ). So what I need is in fact, the normals in “global” space. I thought that, by simply substracting the view vector (“camera data>>view vector”), it would work, but strangely, it doesn’t. I hope that some of you are better informed than me about the vector nodes. :slight_smile: