The GM_GriddedSurface (Figure 23) is a GM_ParametricCurveSurface defined from a rectangular grid in the parameter space. The rows from this grid are control points for horizontal surface curves; the columns are control points for vertical surface curves. The working assumption is that for a pair of parametric coordinates (s, t), that the horizontal curves for each integer offset are calculated and evaluated at "s". This defines a sequence of control points:<br/>#lt;cn(s) : s = 1 ? columns#gt; <br/><br/>From this sequence, a vertical curve is calculated for "s," and evaluated at "t". In most cases, the order of calculation (horizontal-vertical versus vertical-horizontal) does not make a difference. Where it does, the horizontal-vertical order shall be the one used.<br/>