POINTSET _ _ _ _ _ _ _ _ _ _ _ _ type
A curve can be give as a set of precomputed points (a polygon) in 2 or 3 dimensions. Such a point set is a list of points, where each point is a list 2 (or 3) numbers. These numbers are interpreted as (x,y) (or x,y,z) coordinates. All points of one set must have the same dimension.
Also a surface in 3d can be given by precomputed point s, but only on a logically orthogonal mesh: the surface is defined by a list of curves (in 3d) which must have a uniform length. GNUPLOT then will draw an orthogonal mesh by first drawing the given lines, and second connecting the 1st point of the 1st curve with the 1st point of the 2nd curve, that one with the 1st point of the 3rd curve and so on for all curves and for all indexes.