/usr/share/octave/packages/nurbs-1.3.7/nrbcirc.m is in octave-nurbs 1.3.7-1build1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 | function curve = nrbcirc(radius,center,sang,eang)
%
% NRBCIRC: Construct a circular arc.
%
% Calling Sequence:
%
% crv = nrbcirc()
% crv = nrbcirc(radius)
% crv = nrbcirc(radius,center)
% crv = nrbcirc(radius,center,sang,eang)
%
% INPUT:
%
% radius : Radius of the circle, default 1.0
%
% center : Center of the circle, default (0,0,0)
%
% sang : Start angle, default 0 radians (0 degrees)
%
% eang : End angle, default 2*pi radians (360 degrees)
%
% OUTPUT:
%
% crv : NURBS curve for a circular arc.
%
% Description:
%
% Constructs NURBS data structure for a circular arc in the x-y plane. If
% no rhs arguments are supplied a unit circle with center (0.0,0.0) is
% constructed.
%
% Angles are defined as positive in the anti-clockwise direction.
%
% Copyright (C) 2000 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 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/>.
if nargin < 1
radius = 1;
end
if nargin < 2
center = [];
end
if nargin < 4
sang = 0;
eang = 2*pi;
end
sweep = eang - sang; % sweep angle of arc
if sweep < 0
sweep = 2*pi + sweep;
end
if abs(sweep) <= pi/2
narcs = 1; % number of arc segments
knots = [0 0 0 1 1 1];
elseif abs(sweep) <= pi
narcs = 2;
knots = [0 0 0 0.5 0.5 1 1 1];
elseif abs(sweep) <= 3*pi/2
narcs = 3;
knots = [0 0 0 1/3 1/3 2/3 2/3 1 1 1];
else
narcs = 4;
knots = [0 0 0 0.25 0.25 0.5 0.5 0.75 0.75 1 1 1];
end
dsweep = sweep/(2*narcs); % arc segment sweep angle/2
% determine middle control point and weight
wm = cos(dsweep);
x = radius*wm;
y = radius*sin(dsweep);
xm = x+y*tan(dsweep);
% arc segment control points
ctrlpt = [ x wm*xm x; % w*x - coordinate
-y 0 y; % w*y - coordinate
0 0 0; % w*z - coordinate
1 wm 1]; % w - coordinate
% build up complete arc from rotated segments
coefs = zeros(4,2*narcs+1); % nurbs control points of arc
xx = vecrotz(sang + dsweep);
coefs(:,1:3) = xx*ctrlpt; % rotate to start angle
xx = vecrotz(2*dsweep);
for n = 2:narcs
m = 2*n+[0 1];
coefs(:,m) = xx*coefs(:,m-2);
end
% vectrans arc if necessary
if ~isempty(center)
xx = vectrans(center);
coefs = xx*coefs;
end
curve = nrbmak(coefs,knots);
end
%!demo
%! for r = 1:9
%! crv = nrbcirc(r,[],deg2rad(45),deg2rad(315));
%! nrbplot(crv,50);
%! hold on;
%! end
%! hold off;
%! axis equal;
%! title('NURBS construction of several 2D arcs.');
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