The fastest way to render an object is not to render it at all. Object culling provides view-dependent performance improvements by only rendering visible objects. In many cases, only a subset of all objects are visible and a performance gain is expected. Although when all objects are visible, object culling may not improve performance.
Both primitives and globe overlays implement two types of culling.
- View Frustum Culling - Objects outside of the view frustum are not rendered.
- Horizon Distance Culling - Objects that are not visible because they are below the horizon are not rendered.
Technical Details: Primitives are put into a bounding volume hierarchy (BVH)
which is used for hierarchical culling. The BVH is created using a surface area
heuristic. The BVH is efficiently updated when a primitive changes position based on
an algorithm in the 2007 paper Automatic Creation of Object Hierarchies
for Ray Tracing of Dynamic Scenes. Removing primitives, and thus the BVH, is
efficient.
Unfortunately, there is tension between culling and batching. Culling is most effective with lots of small primitives, and batching is most effective with large objects that are generally visible. Ultimately, knowledge of your application should help you decide how to handle culling and batching.