bspderiv.m

强大的nurbs的工具箱 nurbs曲线

function   [dc,dk] = bspderiv(d,c,k)
% 
% Function Name:
% 
%   bspdeval - Evaluate the control points and knot sequence of the derivative
%              of a univariate B-Spline.
% 
% Calling Sequence:
% 
%   [dc,dk] = bspderiv(d,c,k)
% 
% Parameters:
% 
%   d	: Degree of the B-Spline.
% 
%   c	: Control Points, matrix of size (dim,nc).
% 
%   k	: Knot sequence, row vector of size nk.
% 
%   dc	: Control points of the derivative
% 
%   dk	: Knot sequence of the derivative
% 
% Description:
% 
%   Evaluate the derivative of univariate B-Spline, which is itself a B-Spline.
%   This function provides an interface to a toolbox 'C' routine.
[mc,nc] = size(c);
nk = numel(k);
                                                     %
                                                     % int bspderiv(int d, double *c, int mc, int nc, double *k, int nk, double *dc,
                                                     %              double *dk)
                                                     % {
                                                     %   int ierr = 0;
                                                     %   int i, j, tmp;
                                                     %
                                                     %   // control points
                                                     %   double **ctrl = vec2mat(c,mc,nc);
                                                     %
                                                     %   // control points of the derivative
dc = zeros(mc,nc-1);                                 %   double **dctrl = vec2mat(dc,mc,nc-1);
                                                     %
for i=0:nc-2                                         %   for (i = 0; i < nc-1; i++) {
   tmp = d / (k(i+d+2) - k(i+2));                    %     tmp = d / (k[i+d+1] - k[i+1]);
   for j=0:mc-1                                      %     for (j = 0; j < mc; j++) {
       dc(j+1,i+1) = tmp*(c(j+1,i+2) - c(j+1,i+1));  %       dctrl[i][j] = tmp * (ctrl[i+1][j] - ctrl[i][j]);
   end                                               %     }
end                                                  %   }
                                                     %
dk = zeros(1,nk-2);                                  %   j = 0;
for i=1:nk-2                                         %   for (i = 1; i < nk-1; i++)
   dk(i) = k(i+1);                                   %     dk[j++] = k[i];
end                                                  %
                                                     %   freevec2mat(dctrl);
                                                     %   freevec2mat(ctrl);
                                                     %
                                                     %   return ierr;
                                                     % }