Upper panel: Parameterization of a triplet of shears used in this work. For some shears at position X₁, we denote the connecting lines to the two other shears as ϑ_i and the enclosing angle as ϕ. The dashed red lines show the directions of the × projection Eq. (9) for which the three projection axes intersect in X₁. Lower panel: Definition of the geometric quantities involved in the centroid projection Eq. (10). We see that the q vectors connect the centroid of the triangle with the triangles’ vertices.