How to plot the exterior edges only of an alphaShape

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Mustafa Al Homsi 2019-3-18

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/450832-how-to-plot-the-exterior-edges-only-of-an-alphashape

评论： Román Comelli 2022-2-1

I am trying to plot an alphaShape using the code below

x = rand(10,1)*5;
y = rand(10,1)*5;
shape = alphaShape(x,y);
alphas = alphaSpectrum(shape);
shape.Alpha = alphas(1);
ax = app.mapPlt;
plot(shape,'Parent',ax,'EdgeColor','none','LineStyle','--','LineWidth',0.75);

When I plot this shape, the exterior edges are blank. Changing the last line to

plot(shape,'Parent',ax,'EdgeColor','black','LineStyle','--','LineWidth',0.75);

will plot the exterior esdges but it will also plot the the interior edges. Is there a way to plot the exterior edges only?

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回答（1 个）

John D'Errico 2019-3-19

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/450832-how-to-plot-the-exterior-edges-only-of-an-alphashape#answer_366023

编辑：John D'Errico 2019-3-20

在 MATLAB Online 中打开

When you have a problem like this, learn how to investigate what you can do with the class.

x = rand(10,1)*5;
y = rand(10,1)*5;
shape = alphaShape(x,y);
>> methods(shape)
Methods for class alphaShape:
alphaShape          alphaTriangulation  boundaryFacets      inShape             numRegions          plot                volume              
alphaSpectrum       area                criticalAlpha       nearestNeighbor     perimeter           surfaceArea         

methods tells you what methods have been provided. Here, do any of them sound interesting? I hope so.

edges = boundaryFacets(shape)
edges =
     1     4
     4     8
     8     6
     6    10
    10     3
     3     9
     9     2
     2     5
     5     1
     
plot(x(edges),y(edges),'-ro')
hold on
plot(x,y,'.')