A very compelling capability in iBooks Author is its support of 3D objects that your e-book readers can rotate on their iPads. You need to create such a file in the Collada 3D model format (a .dae file) supported by programs such as Adobe Photoshop Extended (version CS5 or later), SketchUp, and Strata 3D.
Convert 3D Models online for free - OBJ, STL, 3DS, Collada, FBX, DXF, LWO, MDL, MD2, MD3 (Quake) and 30 more formats supported. Batch conversion of up to 10 files a time.