How to generate a proper navmesh?


As the title says, I would like to generate a proper and clean navmesh. I’m just getting started and I don’t really know how to do it

I have a model on which I would like to use the VR teleporting. I understood that I have to use a navmesh. But I can’t figure out how to generate it only on the ground. The objects have a complex geometry and my navmesh goes in all directions (on the ground, but also on the walls…). At the narrowest passages, it appears *above *the model. And everything is very fragmented.

Is there a way to set it to be generated in a limited space, only on the ground? or manually draw regions, erase some areas, fill in the gaps…?

Thank you