Ground Plane

A ground plane is the horizontal plane that represents the ground or bottom surface of a space. Ground planes are very useful when rendering because without one, the object in focus appears to be floating (which may be desired in some instances).

A ground plane is not needed if you are using a three-dimensional table or other surface. The table will act as the ground plane, making it unnecessary. If this is the case, uncheck the Ground Plane box.

Adding a ground plane makes this drivetrain look like it is resting on a surface

Flatten Ground

The Flatten Ground option stretches out the ground plane by a certain amount. This is dependent on the Ground Scale, which you can adjust by selecting the Position icon. Be careful when using this, however. An improperly-scaled ground plane will mess up the HDRI, as seen below.

If you are using a table or other similar surface, make sure that Flatten Ground isn't selected. Unless you know what you're doing, it is highly recommended that you stay away from this.

FTC 11115 automatic ball turret

Flatten ground is a useful feature when you want the robot to rest on the ground plane of the HDRI, as seen below. The HDRI must be properly scaled or else your robot may look like it is floating. Or, another technique that is in the render below is adding a heavy depth of field to mask an HDRI that isn't scaled perfectly.

FTC 18253 Ultimate Goal Robot rendered by FTC 18219

Reflections

The Reflections option allows for the CAD model to be reflected onto the ground plane. How much it is reflected depends on the roughness, which can be any number between 0 and 1. A roughness closer to 0 will result in a more reflective ground plane, while a roughness closer to 1 will result in a less reflective and more rough ground plane.

FTC 9614 Ultimate Goal Robot with a reflective ground plane