Contours to polygons
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From: Sujit on 24 Mar 2010 15:11 How can I quickly convert contours to polygons? i.e. How can I quickly extract all polygons (x and y) from C, where [C,g] = contour(Z); ? The structure of C looks complicated -- anyone have something handy?
From: Bruno Luong on 24 Mar 2010 15:57 "Sujit " <kirpekar(a)gmail.com> wrote in message <hodo49$t4u$1(a)fred.mathworks.com>... > How can I quickly convert contours to polygons? i.e. How can I quickly extract all polygons (x and y) from C, where [C,g] = contour(Z); ? > > The structure of C looks complicated -- anyone have something handy? A = peaks(40); v=[-10:10] c = contourc(A, v); struct = contour2poly(c) %% function cstruct = contour2poly(c) idxlabel = 1; l = 1; cstruct = struct('level', {}, 'x', {}, 'y', {}); while idxlabel <= size(c,2) n = c(2,idxlabel); cstruct(l).x = c(1,idxlabel+(1:n)); cstruct(l).y = c(2,idxlabel+(1:n)); cstruct(l).level = c(1,idxlabel); l = l+1; idxlabel = idxlabel+n+1; end end % contour2poly % Bruno
From: Walter Roberson on 24 Mar 2010 16:09 Sujit wrote: > How can I quickly convert contours to polygons? i.e. How can I quickly > extract all polygons (x and y) from C, where [C,g] = contour(Z); ? > > The structure of C looks complicated -- anyone have something handy? Take the other approach -- go into the handle that is returned! polycells = arrayfun( @(ch) horzcat( get(ch,'XData'), get(ch,'YData')), get(g,'Children'),'Uniform',0); %g is the handle from contour() will return a cell array, each of which contains an array of coordinate pairs, X in column 1 and Y in column 2. If that's not exactly how you you would like the output, you can adjust to suit your needs. Note that the fetched XData and YData will be column vectors.
From: Walter Roberson on 24 Mar 2010 16:27 Bruno Luong wrote: > "Sujit " <kirpekar(a)gmail.com> wrote in message > <hodo49$t4u$1(a)fred.mathworks.com>... >> How can I quickly convert contours to polygons? > function cstruct = contour2poly(c) > while idxlabel <= size(c,2) Ah, but can you code it without an explicit loop? ;-) (I have a mental outline for a recursive approach, and a hack in mind that would use arrayfun...)
From: Bruno Luong on 24 Mar 2010 19:03
Walter Roberson <roberson(a)hushmail.com> wrote in message > Ah, but can you code it without an explicit loop? ;-) > > (I have a mental outline for a recursive approach, and a hack in mind that > would use arrayfun...) Of course you are right Walter, it is straightforward to convert while-loop to equivalent recursive call: function cstruct = contour2poly(c) if isempty(c) cstruct = struct('level', {}, 'x', {}, 'y', {}); else n = c(2,1); idx = 2:n+1; cstruct = [struct('level', c(1,1), 'x', c(1,idx), 'y', c(2,idx)) ... contour2poly(c(:,n+2:end))]; end end % contour2poly % Bruno |