T-vertices

File:Example of T-vertices in Blender.png

T-vertices is a term used in computer graphics to describe a problem that can occur during mesh refinement or mesh simplification. The most common case occurs in naive implementations of continuous level of detail, where a finer-level mesh is "sewn" together with a coarser-level mesh by simply aligning the finer vertices on the edges of the coarse polygons. The result is a continuous mesh, however due to the nature of the z-buffer and certain lighting algorithms such as Gouraud shading, visual artifacts can often be detected.[http://www.cs.princeton.edu/courses/archive/spr98/cs598d/lectures/alejo/ Frequent Mesh Problems, www.cs.princeton.edu]

File:Example of T-vertices in Blender after applying a subdivision modifier.png

Some modeling algorithms such as subdivision surfaces will fail when a model contains T-vertices.