Question about convhull code

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Ingo Rück
Ingo Rück 2017-7-19
编辑： Jan 2017-7-19
Hello everyone,
I'm using the function convhull to create a better looking hill chart. For that purpose I need to know how Matlab determines at which point the hull-curve should start. The documentation of convhull doesnt tell me anything and I'm too unexperienced to dig into the code of the function itself (that and I dont know when something is considered "reverse engineering", which might be illegal anyway).
  2 个评论
Image Analyst
Image Analyst 2017-7-19
Please include some screen shots. You can edit any program and see what it does, at least to some extent, for example
>> edit convhull.m
Perhaps you'd be interested in the boundary() or envelope() function instead - not sure until we see your data.
Jan
Jan 2017-7-19
编辑：Jan 2017-7-19
@Ingo: You have mentioned in your other thread, that you need the hull start with the smallest X and Y position. By the way: Whenever you post multiple thread about one problem, add a link to the thread in the other forum also. Otherwise such "cross-posting" can waste the time of the ones, who write an already given answer. Thanks.

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Jan
Jan 2017-7-19
编辑：Jan 2017-7-19
Reading the M- and C-files is considered to be legal.
You can resort the output easily to be sure that it has the wanted order:
K = convhull(X,Y);
C = [X(K), Y(K)];
[~, Index] = sortrows(C); % Only the first entry matters
if Index(1) ~= 1 % Reordering required
K = circshift(K, -Index(1) + 1);
end
Now the first index in K is the position with the smallest X and Y values.
In the current Matlab version, K is ordered as you want it. But you cannot be sure if this is the general case, such that the above check is safer.

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