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nrbruled.m

%% Copyright (C) 2003 Mark Spink
%% 
%% This program is free software; you can redistribute it and/or modify
%% it under the terms of the GNU General Public License as published by
%% the Free Software Foundation; either version 2 of the License, or
%% (at your option) any later version.
%% 
%% This program is distributed in the hope that it will be useful,
%% but WITHOUT ANY WARRANTY; without even the implied warranty of
%% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
%% GNU General Public License for more details.
%% 
%% You should have received a copy of the GNU General Public License
%% along with this program; if not, see <http://www.gnu.org/licenses/>.

function srf = nrbruled(crv1, crv2)

% NRBRULED: Construct a ruled surface between two NURBS curves.
% 
% Calling Sequence:
% 
%   srf = nrbruled(crv1, crv2)
% 
% Parameters:
% 
%   crv1          : First NURBS curve, see nrbmak.
% 
%   crv2          : Second NURBS curve, see nrbmak.
% 
%   srf           : Ruled NURBS surface.
% 
% Description:
% 
%   Constructs a ruled surface between two NURBS curves. The ruled surface is
%   ruled along the V direction.
% 
% Examples:
% 
%   Construct a ruled surface between a semicircle and a straight line.
% 
%   cir = nrbcirc(1,[0 0 0],0,pi);
%   line = nrbline([-1 0.5 1],[1 0.5 1]);
%   srf = nrbruled(cir,line);
%   nrbplot(srf,[20 20]);

%  D.M. Spink
%  Copyright (c) 2000.

if iscell(crv1.knots) | iscell(crv2.knots)
  error('Both NURBS must be curves');
end

% ensure both curves have a common degree
d = max([crv1.order, crv2.order]);
crv1 = nrbdegelev(crv1, d - crv1.order);
crv2 = nrbdegelev(crv2, d - crv2.order);

% merge the knot vectors, to obtain a common knot vector
k1 = crv1.knots;
k2 = crv2.knots;
ku = unique([k1 k2]);
n = length(ku);
ka = [];
kb = [];
for i = 1:n
  i1 = length(find(k1 == ku(i)));
  i2 = length(find(k2 == ku(i)));
  m = max(i1, i2);
  ka = [ka ku(i)*ones(1,m-i1)];
  kb = [kb ku(i)*ones(1,m-i2)];
end
crv1 = nrbkntins(crv1, ka);
crv2 = nrbkntins(crv2, kb);

coefs(:,:,1) = crv1.coefs;
coefs(:,:,2) = crv2.coefs;
srf = nrbmak(coefs, {crv1.knots, });


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