Decimate Mesh

Decimation removes geometry from an existing mesh without rebuilding the topology by hand. Collapse-style decimation, the common quadric error method behind many tools, removes edges that least affect the surface mathematically. Planar decimation removes unnecessary triangles on nearly flat surfaces, which is excellent for hard-surface props, buildings and faceted rocks. Un-subdivide tries to reverse subdivision patterns and is useful only when the dense mesh came from an orderly subdivided base.

The safe cases are static props, background scatter and LOD versions where deformation is irrelevant. A low poly rock, crate, ruined wall or city block can often lose 40 to 70 percent of its triangles if the silhouette is protected. The unsafe cases are faces, hands, elbows, knees and any skinned character area where edge loops drive deformation. Decimation there can collapse loops that an animator needs, causing pinching that no normal map can hide.

The practical workflow is incremental. Duplicate the mesh, apply transforms, triangulate if the target engine will triangulate anyway, then reduce in small steps while watching the outline from the camera distances where the asset appears. Lock UV borders and material seams when the tool allows it, because collapsing a UV island edge can create texture stretching even if the geometry looks fine in solid view. After decimation, recalculate normals and inspect flat-shaded faces for accidental smoothing changes.

Decimation is different from full polycount optimization. It cuts triangles, but it will not automatically reduce draw calls, merge materials, resize textures or create a clean riggable topology. Use it as a fast reduction step for static geometry, as an LOD generator input, or as a first pass before manual cleanup. If the mesh will animate close to camera, use retopology instead and bake high-frequency detail from the source.