In 3D computer graphics, hidden surface determination (also known as hidden surface removal (HSR), occlusion culling (OC) or visible surface determination (VSD)) is the process used to determine which surfaces and parts of surfaces are not visible from a certain viewpoint. A hidden surface determination algorithm is a solution to the visibility problem, which was one of the first major problems in the field of 3D computer graphics. The process of hidden surface determination is sometimes called hiding, and such an algorithm is sometimes called a hider. The analogue for line rendering is hidden line removal. Hidden surface determination is necessary to render an image correctly, so that one cannot look through walls in virtual reality.

Since you can't see the hidden surface, from your point of view, then the graphics system should not (normally) display the hidden surface except (optionally) to display dashed lines for hidden edges and dashed dimension lines to hidden edges.

Posined gas.

an anti-aliased hidden surface method

They are mostly hidden underwater because nothing has yet made them erupt and come to the surface.