The 3D models in PhotoModeler have an arbitrary coordinate system until set by you.
If you export a model without the coordinate system set up (i.e. scale/rotate/translate or control points) the exported model will not be dimensionally accurate.
You may also find that the model exported by PhotoModeler is rotated incorrectly relative to the starting view you want or the world you are building. Use an axes-based rotation to clean this up. See Importing and Setting Up Coordinate Systems.