The ground plane represents an up direction in model space, and provides a visual cue for model scale. You can display reflections of your model in the ground plane, giving the view a showroom floor effect.
The ground plane orientation is established in relation to the ViewCube Bottom and remains parallel to it. Positive of negative positional values are in relation to the ViewCube. To reorient the ground plane, modify the ViewCube orientation.
When rotating the model using the view controls, the ground plane relationship to the model remains intact. When viewing the model from beneath the ground plane, the plane is hidden until the camera position is above the ground plane.
- Position the ground plane origin.
- Offset the ground plane from the origin.
- Specify the ground plane color.
- Specify the ground plane opacity.
- Specify the major and minor grid lines and their visibility.
- Specify the Reflection parameters for amount of reflection, blur, and blur fall-off.
The ground plane settings changes are maintained in document settings. Each document can have a unique ground plane setting. At any time, you can temporarily override visibility of the Ground Plane on the View tab 
Appearance panel.
You can display other effects, such as shadows and reflections, with the ground plane visible or not visible.
Ground plane On and Off changes are session-based. Changes to the Ground Plane Settings are document-based, and are preserved with the document upon Save.