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87. TETRAPODS These strange looking objects are called tetrapods, and are used for breakwaters and retaining walls in coastal areas. A tetrapod is an object having four ‘feet’ radiating from the centre. If we think of a stylized tetrapod having four equal segments radiating from a central point, the outward tips of the segments form the vertices of a regular tetrahedron. In fact, if we visualize this tetrahedron together with the defining internal segments, we have a 3-dimensional picture of the 4-dimensional analogue of the tetrahedron – the 4-dimensional simplex. (We work by analogy here: think of a triangle in the plane with lines to the vertices from the centroid. Visualize this in 3-space – you should see a tetrahedron.)
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