Geometry
This factor can be found at numerous locations throughout Cinema 4D when importing or exporting foreign formats. Therefore, don’t be surprised if the term ,export’ is used if this factor is seen in an import function (this factor is explained as a whole here).
This factor lets you scale files upon import/export, i.e., practically all relevant numerical values saved in the file or those to be saved will be multiplied by this factor and then saved - or interpreted when loaded.
The unit at the right in turn defines how upon
- Import the numerical value saved in the file is converted to the current Cinema 4D unit. Example: if an X value of 1 is saved in the file and you define Feet, the X value will be converted to 30.48 cm in Cinema 4D (if centimeters are defined by default in Cinema 4D).
- Export numerical values are saved in the file. Example: an X value is set to 100 cm in Cinema 4D. If you define Feet for export, the exported file will save a numerical value of 3.281 (1 meter = 3.281 feet).
More information about units and scaling can be found in the Project Scale section.
You have the following options for exporting UV coordinates:
No UV coordinates will be exported.
The UV coordinates will be exported as they were saved in the UVW tag, i.e., unmodified. If multiple UVW tags exist, only the first will be imported.
These options mirror the UV coordinates correspondingly.
UV coordinates will be exported vertically and horizontally mirrored .
Use this setting to define if vertex Normals should be imported/exported. Phong tags can be generated for import.
Enable this option if you want to export colors saved in a Vertex Color tag. Exported colors can, for example, be read by Meshlab and ZBrush.
The OBJ format always assumes object axes from the world origin. Other object positions or orientations in the OBJ file are achieved only via object point positions. Once such a file is imported it can be modified as usual (the 
Axis Center command can be helpful).
Since the OBJ format is such a commonly used format and different applications use different axis systems (with almost any imaginable axis combination, even with the Y axis pointing to the rear), these settings let you adjust the axes accordingly.
When importing certain OBJ files, for example, an object can literally be stood on its head. Enabling the Flip Y Axis option can prevent this from happening. Or you can switch the X and Y axes when exporting to a particular application because it has a different axis system. To do so, simply enable the Swap X and Y Axes option.
If this option is enabled, all polygon Normals will be flipped upon import/export.
Here you can define if N-Gons should be resolved, i.e., broken down into triangles or quads and exported. This occurs analog to the 
Remove N-gons command.
N-Gons should always be resolved if the target application does not work with N-Gons.
The OBJ format uses several methods for grouping polygons, primarily Groups and Objects (in the .obj files they only differ by one letter: either a g or an o will be placed before the group or object name). Some programs interpret groups and objects differently while others don't differentiate at all.
If this option is enabled, Cinema 4D will declare each object as a group for export (primarily suited for export to 3ds Max), otherwise the objects will be declared as objects.