Delete triangulations outside the outline polygon and z value manipulation

Question

zzzzz Sap 2011-4-4

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https://ww2.mathworks.cn/matlabcentral/answers/4677-delete-triangulations-outside-the-outline-polygon-and-z-value-manipulation

评论： Yonni f 2022-10-26

I have an outline polygon traced using impoly, over an image of an outline. When I triangulate it using delaunay command, triangulations extend outside the polygon. how to delete these unwanted triangles, and then manipulate the z values of the polygon, to change its orientation? I'm using Matlab R2008a

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Answer 1

Paul Rötzer 2022-10-17

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I know the answer comes very late but i struggled with the same problem today.

For newer version of matlab the following should work:

% P contains the points on outline of polyshape 
polyin = polyshape(P);
EdgeConstraint = [(1:length(P))' [(2:length(P))'; 1]];
DT = delaunayTriangulation(P, EdgeConstraint)
%% remove outside triangles
C = incenter(DT);
TF = isinterior(polyin, C);
InsideTriangles = DT.ConnectivityList(TF, :);

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Yonni f 2022-10-26

Amazing. I was just strugging on the same thing and I found your response to a decade old post.

To ellaborate a bit more on Paul's answer, I edited the triangulation by calling a new structure called dts and then removing the connections outside the border:

dts = struct('Points', DT.Points, 'ConnectivityList', DT.ConnectivityList);

dts.ConnectivityList(~TF, :) = [];

x=triangulation(dts.ConnectivityList, dts.Points);

triplot(x);

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