Spire Tetrahedron

A spire tetrahedron is a long, thin tetrahedron with three vertices clustered near one endpoint and the fourth near a distant endpoint (Cheng et al. 2012, p. 25; Hannukainen et al. 2017, p. 3).

In this qualitative classification, it is also called a needle tetrahedron. In the degenerate limit, the three clustered vertices coalesce, and the shape approaches a line segment. The name is used in descriptions of tetrahedral mesh shape and mesh quality.