A vector of vertex indices, i.e. integer values between 0 and the length of the vertex vectors, representing the *second* vertex of a triangle. For example, `{i[m], j[m], k[m]}`  together represent face m (triangle m) in the mesh, where `j[m] = n` points to the triplet `{x[n], y[n], z[n]}` in the vertex arrays. Therefore, each element in `j` represents a point in space, which is the second vertex of a triangle.

A vector of vertex indices, i.e. integer values between 0 and the length of the vertex vectors, representing the *third* vertex of a triangle. For example, `{i[m], j[m], k[m]}` together represent face m (triangle m) in the mesh, where `k[m] = n` points to the triplet  `{x[n], y[n], z[n]}` in the vertex arrays. Therefore, each element in `k` represents a point in space, which is the third vertex of a triangle.

Sets the text elements associated with the vertices. If trace `hoverinfo` contains a *text* flag and *hovertext* is not set, these elements will be seen in the hover labels.

Sets the Delaunay axis, which is the axis that is perpendicular to the surface of the Delaunay triangulation. It has an effect if `i`, `j`, `k` are not provided and `alphahull` is set to indicate Delaunay triangulation.

Determines how the mesh surface triangles are derived from the set of vertices (points) represented by the `x`, `y` and `z` arrays, if the `i`, `j`, `k` arrays are not supplied. For general use of `mesh3d` it is preferred that `i`, `j`, `k` are supplied. If *-1*, Delaunay triangulation is used, which is mainly suitable if the mesh is a single, more or less layer surface that is perpendicular to `delaunayaxis`. In case the `delaunayaxis` intersects the mesh surface at more than one point it will result triangles that are very long in the dimension of `delaunayaxis`. If *>0*, the alpha-shape algorithm is used. In this case, the positive `alphahull` value signals the use of the alpha-shape algorithm, _and_ its value acts as the parameter for the mesh fitting. If *0*,  the convex-hull algorithm is used. It is suitable for convex bodies or if the intention is to enclose the `x`, `y` and `z` point set into a convex hull.