How to create a boundary along the edges for 3d plot?

Question

Shiv Karpoor 2022-3-8

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https://ww2.mathworks.cn/matlabcentral/answers/1666779-how-to-create-a-boundary-along-the-edges-for-3d-plot

评论： Shiv Karpoor 2022-3-9

采纳的回答： Benjamin Thompson

points435.xlsx

在 MATLAB Online 中打开

Hello MATLAB Community,

I am having a problem creating boundary line for the point cloud as shown in the below image in RED colour.

(Note: the below image is taken from MATLAB blogs)

here is my code and excel document consisting of around 14000 points:

A = readmatrix('points435');
plot3(A(:,1),A(:,2),A(:,3),'.')

My code runs a part of the problem I am working on.

The image shown above is different from the results of the code attached.

I only need to trace a line along the boundary of the point cloud which is 3d.

Can anyone please help me with any suggestions.

Thank you in advance!!

I really appreciate your help.

Kind regards,

Shiv

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Answer 1

Benjamin Thompson 2022-3-8

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https://ww2.mathworks.cn/matlabcentral/answers/1666779-how-to-create-a-boundary-along-the-edges-for-3d-plot#answer_913119

There is a function called "boundary" that should work for you. Type "help boundary" or "doc boundary" for more information.

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Benjamin Thompson 2022-3-8

编辑：Benjamin Thompson 2022-3-8

Boundary supports 3D problems also. In that case the return value specifies the set of triangles enclosing your shape. But you problem is really 2D since the third dimension is constrained to 435. Here is how to construct the boundary of your 2D data set in 3D space:

>> data = xlsread('points435.xlsx');

>> figure, plot3(data(:,1), data(:,2), data(:,3));

>> min(data(:,1))

ans =

-7.926606985093684

>> min(data(:,2))

ans =

-6.864643014906309

>> min(data(:,3))

ans =

435

>> max(data(:,3))

ans =

435

>> k = boundary(data(:,1), data(:,2));

>> hold on, plot3(data(k,1), data(k,2), 435*ones(size(k,1),1), 'r-')

>> grid on;

>>

If you are looking for something different look over all the options that boundary offers. Adjusting the shrink factor parameter "s" may help you tweak the output some.

Shiv Karpoor 2022-3-9