Find borders of a truth map

Question

Daniel Cleveland 2015-12-15

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/260331-find-borders-of-a-truth-map

评论： Daniel Cleveland 2015-12-15

采纳的回答： Guillaume

在 MATLAB Online 中打开

Hi,

I have an array

truth_map =

 [0 0 0 0 0 0 0 0 1 1 ; 
0 0 0 0 0 0 0 1 1 ;
0 0 0 0 0 0 1 1 1 ;
0 0 0 0 0 1 1 1 0 ;
0 0 0 0 1 1 1 1 0 ;
1 1 1 1 0 0 0 0 0 ;
1 1 1 1 0 0 0 0 0 ;
1 1 1 1 0 0 0 0 0 ;
1 1 1 0 0 0 0 0 0 ;
1 1 0 0 0 0 0 0 0 ; ]

Which I want to make look like this:

truth_map =

 [0 0 0 0 0 0 0 0 1 0 ; 
0 0 0 0 0 0 0 1 0 ;
0 0 0 0 0 0 1 0 1 ;
0 0 0 0 0 1 0 1 0 ;
0 0 0 0 1 1 1 1 0 ;
1 1 1 1 0 0 0 0 0 ;
0 0 0 1 0 0 0 0 0 ;
0 0 0 1 0 0 0 0 0 ;
0 0 1 0 0 0 0 0 0 ;
0 1 0 0 0 0 0 0 0 ; ]

This is trivial to do by hand for small arrays but my array is 1000x1000 and the area's are randomly shaped.

What would be a good way to just get an array of the borders?

Thanks, Daniel

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Answer 1

Guillaume 2015-12-15

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链接

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https://ww2.mathworks.cn/matlabcentral/answers/260331-find-borders-of-a-truth-map#answer_203271

在 MATLAB Online 中打开

The way you've defined your edges they correspond to either transition from 0 to 1 or from 1 to 0 when scanning from left to right or top to bottom. This is easily detected by diff:

m =  [0 0 0 0 0 0 0 0 1 1 ; 
      0 0 0 0 0 0 0 0 1 1 ;
      0 0 0 0 0 0 0 1 1 1 ;
      0 0 0 0 0 0 1 1 1 0 ;
      0 0 0 0 0 1 1 1 1 0 ;
      0 1 1 1 1 0 0 0 0 0 ;
      1 1 1 1 1 0 0 0 0 0 ;
      1 1 1 1 1 0 0 0 0 0 ;
      1 1 1 1 0 0 0 0 0 0 ;
      1 1 1 0 0 0 0 0 0 0 ; ]
m2 = [zeros(1, size(m, 2)); diff(m) == 1] | ... 0 to 1 from top to bottom
     [diff(m) == -1; zeros(1, size(m, 2))] | ... 1 to 0 from top to bottom
     [zeros(size(m, 1), 1), diff(m, [], 2) == 1] | ... 0 to 1 from left to right
     [diff(m, [], 2) == -1, zeros(size(m, 1), 1)] % 1 to 0 from left to right