This is a Pro only feature.
The OBJ Export Options dialog box contains options for exporting OBJ files.
Export only current selection
The Export only current selection checkbox is used to export the currently selected geometry. The entire SketchUp model is exported when there is no selection. Additionally, the entire model is exported when this checkbox is not checked.
Triangulate all faces
The Triangulate all faces checkbox is used to break the output into triangles instead of multi-sided faces.
Export two-sided faces
The Export two-sided faces checkbox is used to export faces twice, once for the front and once for the back. This option doubles the number of polygons in the resulting OBJ file and can slow down rendering. However, this option ensures that your model will appear more like it appears in SketchUp. Both faces will always render, and materials applied to front and back faces are preserved.
The Export edges checkbox is used to write SketchUp line entities as OBJ line entities. Edges are ignored when this checkbox is not checked. Usually this checkbox is not checked because most applications will ignore edges on import.
The Materials section of OBJ Export Options Dialog box is used to identify how materials will be exported.
Export texture maps
Check the Export texture maps checkbox to export textures with your OBJ file.
The Scale section OBJ Export Options Dialog box is used to identify the scale used in the OBJ output.
Swap YZ coordinates (Y is up)
The Swap YZ coordinates check box is used to output the model with the vertical direction as Y. This orientation is the default orientation for some applications, such as Maya. Do not check this box if you want your model to be output with the Z axis in the vertical direction, such as when using 3D Studio Max.
The units drop-down list is used to determine the unit size in the OBJ output. The Model Units setting is used to select the units that are being used in SketchUp.