In the specification tree, select an
environment wall (or select it directly in the 3D window).
display the contextual menu then clear Wall Active. The
selected wall is grayed in the specification tree and is not taken into
account at rendering time, as shown in the example below:
Only the edges of the deactivated wall are
displayed in the environment representation except if you specified
that inactive environments are displayed (in Tools > Options >
Real Time Rendering > Display > Rendering).
Geometry shadows are projected onto environment flat walls.