/usr/share/octave/packages/geometry-1.7.0/polygons2d/polygonSubcurve.m is in octave-geometry 1.7.0-1build1.
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## Copyright (C) 2012 Adapted to Octave by Juan Pablo Carbajal <carbajal@ifi.uzh.ch>
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## -*- texinfo -*-
## @deftypefn {Function File} {@var{poly2} =} polygonSubcurve (@var{polygon}, @var{pos0},@var{pos1})
## Extract a portion of a polygon
##
## Create a new polyline, by keeping vertices located between positions
## @var{pos0} and @var{pos1}, and adding points corresponding to positions @var{pos0} and
## @var{pos1} if they are not already vertices.
##
## Example:
## @example
## Nv = 100;
## poly = circleAsPolygon ([10 20 30], Nv);
## poly2 = polygonSubcurve (poly, 15, 65);
## drawPolyline (poly2);
## @end example
##
## @seealso{polygons2d, polylineSubcurve}
## @end deftypefn
function res = polygonSubcurve(poly, t0, t1)
# number of vertices
Nv = size(poly, 1);
if t0<t1
# format positions
t0 = max(t0, 0);
t1 = min(t1, Nv);
end
# indices of extreme vertices inside subcurve
ind0 = ceil(t0)+1;
ind1 = floor(t1)+1;
# get the portion of polyline between 2 extremities
if t0<t1
if ind1<=Nv
res = poly(ind0:ind1, :);
else
res = poly(1, :);
end
else
res = poly([ind0:end 1:ind1], :);
end
# add first point if it is not already a vertex
if t0~=ind0-1
res = [polygonPoint(poly, t0); res];
end
# add last point if it is not already a vertex
if t1~=ind1-1
res = [res; polygonPoint(poly, t1)];
end
endfunction
%!demo
%! Nv = 100;
%! poly = circleAsPolygon ([10 20 30], Nv);
%! poly2 = polygonSubcurve (poly, 15, 65);
%!
%! drawPolygon (poly,'k-o',"MarkerSize",3);
%! hold on
%! drawPolyline (poly2,'r.',"linewidth",2);
%! hold off
%! axis square
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