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## Copyright (C) 2002 Etienne Grossmann <etienne@egdn.net>
##
## 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 3 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/>.
## v = vrml_ellipsoid (moment, col) - Ellipsoid
##
## moment : 3x3 : Define elipsoid by x'*moment*x = 1
## or 3 : use diag(moment)
## or 1 : use diag(moment([1,1,1])) default : eye(3)
##
## col : 3 : Color default : [0.3 0.4 0.9]
##
function v = vrml_ellipsoid(moment, col)
if nargin<2 || isempty (col) || isnan (col), col = [0.3 0.4 0.9];
else
error ("vrml_ellipsoid : col has size %d x %d. This won't do\n",size(col));
## keyboard
end
col = col' ;
if nargin<1 || isempty (moment), moment = eye(3),
elseif all (size (moment) == 3), # Do nothing
elseif prod( size (moment)) == 3, moment = diag (moment);
elseif length (moment) == 1, moment = moment*eye(3);
else
error ("vrml_ellipsoid : moment has size %d x %d. This won't do\n",size(moment));
## keyboard
end
[u,d,v] = svd (moment);
d = diag(d);
d(find(d)) = 1 ./ nze (d) ;
[r,a] = rotparams (u');
v = sprintf (["Transform {\n",...
" translation 0 0 0\n",...
" rotation %8.3g %8.3g %8.3g %8.3g\n",...
" scale %8.3g %8.3g %8.3g\n",...
" children [\n",...
" Shape {\n",...
" appearance Appearance {\n",...
" material Material {\n",...
" diffuseColor %8.3g %8.3g %8.3g\n",...
" emissiveColor %8.3g %8.3g %8.3g\n",...
" }\n",...
" }\n",...
" geometry Sphere {}\n",...
" }\n",...
" ]\n",...
"}\n",...
],...
r,a,...
d,...
col,...
col/20);
endfunction
## Example
## d0 = sort (1+2*rand(1,3));
## d0 = 1:3;
## rv = randn (1,3);
## uu = rotv (rv);
## dd = diag (1./d0);
## mm = uu*dd*uu';
## vrml_browse ([vrml_frame ([0,0,0],uu',"col",eye(3),"scale",2*d0), vrml_ellipsoid(mm)]);
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