Can anyone help me in this code ?

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L K 2017-3-15

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评论： L K 2017-3-16

%To Calculate the points which lie inside and outside Tolerance
[in,on] = inpolygon(real,imag,xch_larger,ych_larger);
p=numel(real(in))
%disp(in)
q=numel(real(on))
%disp(on)
r=numel(real(~in))

i want a msg to be displayed when r>=0

i have put this statement

if r >= 0;
    msgbox('So-n-so','Detected Object','error');
else
    msgbox('So-n-so','Detected Object');
end

But the problem i am facing is, even if the value is r<=0 Still it displays the first msg, it does not go in the else part... what is problem ?

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Answer 1

Guillaume 2017-3-15

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编辑：Guillaume 2017-3-15

在 MATLAB Online 中打开

I strongly suspect that you want the number of query points in, on and outside the polygon, which you'll never get with numel (See comment to Image Analyst's answer). I suspect this is what you want:

p = sum(in);  %number of points inside or on the polygon
q = sum(on);  %number of points on the polygon
r = sum(~in); %number of points outside the polygon

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Guillaume 2017-3-15

I've just noticed that real and imag are variable names, and not the functions real and imag. So yes, your code would work (but be slightly slower).

However, I would encourage you to rename these two variables to something that is not a standard matlab function. Not only would it avoid this sort of confusion, it would prevent potential bugs (where you try to use the function and ends up indexing into the variable instead).

L K 2017-3-16

Thanx for the valuable info :) I did the changes

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Answer 2

Image Analyst 2017-3-15

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numel() returns the number of elements in an array. Why do you think that should EVER be negative?

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L K 2017-3-15

Ok Ya i got my mistake... if was suppose to be r>0... and the other condition would be true when r=0... I just realized it..

Guillaume 2017-3-15

编辑：Guillaume 2017-3-15

And since in and on are logical arrays, all those real(something) are also completely pointless.

And since in and ~in obviously have the same numbers of elements, p and r will always be equal.

"and the other condition would be true when r=0"

And since the number of elements in in and on is the same as the number of elements in the input, the only way that r can be 0 is if you pass zero query points.

Really, the problem is not with the if but with everything that is before!

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