Unity objects and terrain exporter

Question

I am trying to export a terrain and models in a unity evironment to an .obj file. I have a code which exports a terrain properly and also one which exports the models properly. When I try to combine them, the models (inside unity!) jump to the corner of my terrain. To get the data of the terrain I use Terrain.activeTerrain, and for the models I use Selection.gameobjects. I do not alter the environment through my script.
Does anyone know whats going wrong here?