Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / nurbs-1.3.6 / nrbextract.m

diff --git a/octave_packages/nurbs-1.3.6/nrbextract.m b/octave_packages/nurbs-1.3.6/nrbextract.m
new file mode 100644 (file)
index 0000000..69e01c1
--- /dev/null
+++ b/octave_packages/nurbs-1.3.6/nrbextract.m
@@ -0,0 +1,87 @@
+function crvs = nrbextract(srf)
+
+%
+% NRBEXTRACT: construct NURBS curves by extracting the boundaries of a NURBS surface, or NURBS surfaces by extracting the boundary of a NURBS volume.
+% 
+% Calling Sequence:
+% 
+%   crvs = nrbextract(surf);
+% 
+% INPUT:
+% 
+%   surf        : NURBS surface or volume, see nrbmak.
+% 
+% OUTPUT: 
+% 
+%   crvs        : array of NURBS curves or NURBS surfaces extracted.
+% 
+% Description:
+% 
+%  Constructs either an array of four NURBS curves, by extracting the boundaries
+%  of a NURBS surface, or an array of six surfaces, by extracting the boundaries
+%  of a NURBS volume. The new entities are ordered in the following way
+%
+%    1: U = 0
+%    2: U = 1
+%    3: V = 0
+%    4: V = 1
+%    5: W = 0 (only for volumes)
+%    6: W = 1 (only for volumes)
+%
+%    Copyright (C) 2010 Rafael Vazquez
+%
+%    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/>.
+
+if (~iscell (srf.knots))
+  error('The boundary information is only extracted for NURBS surfaces or volumes');
+end
+
+if (numel (srf.knots) == 2)
+  for ind = 1:2
+    ind2 = mod (ind, 2) + 1;    %ind2 = [2 1];
+    bnd1 = (ind - 1) * 2 + 1;
+    bnd2 = (ind - 1) * 2 + 2;
+    if (ind == 1)
+      coefs1 = squeeze (srf.coefs(:,1,:));
+      coefs2 = squeeze (srf.coefs(:,end,:));
+    elseif (ind == 2)
+      coefs1 = squeeze (srf.coefs(:,:,1));
+      coefs2 = squeeze (srf.coefs(:,:,end));
+    end
+    crvs(bnd1) = nrbmak (coefs1, srf.knots{ind2});
+    crvs(bnd2) = nrbmak (coefs2, srf.knots{ind2});
+  end
+elseif (numel (srf.knots) == 3)
+  for ind = 1:3
+    inds = setdiff (1:3, ind);
+    bnd1 = (ind - 1) * 2 + 1;
+    bnd2 = (ind - 1) * 2 + 2;
+    if (ind == 1)
+      coefs1 = squeeze (srf.coefs(:,1,:,:));
+      coefs2 = squeeze (srf.coefs(:,end,:,:));
+    elseif (ind == 2)
+      coefs1 = squeeze (srf.coefs(:,:,1,:));
+      coefs2 = squeeze (srf.coefs(:,:,end,:));
+    elseif (ind == 3)
+      coefs1 = squeeze (srf.coefs(:,:,:,1));
+      coefs2 = squeeze (srf.coefs(:,:,:,end));
+    end
+    crvs(bnd1) = nrbmak (coefs1, {srf.knots{inds(1)} srf.knots{inds(2)}});
+    crvs(bnd2) = nrbmak (coefs2, {srf.knots{inds(1)} srf.knots{inds(2)}});
+  end
+else
+  error ('The entity is not a surface nor a volume')
+end
+
+end