How to find when a surface deviates from other surface(s)

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A il 18 Apr 2014

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https://it.mathworks.com/matlabcentral/answers/126198-how-to-find-when-a-surface-deviates-from-other-surface-s

Commentato: Star Strider il 19 Apr 2014

Hi guys,

I have 3 surfaces. I want to find out values for x and y, where each of the three surfaces deviates from the other two by more than 0.5 value on the z axis. Is this a simple enough thing?

I can imagine it being super easy to do with only two surfaces because you could just substract one from the other. But how do I do it with 3 surfaces? Any ideas?

Ideally, I'd like to see [x,y] points for each surface where it deviates from other surfaces on z-axis by > 0.5.

It would be great to be able to graphically see this 'deviation' as well perhaps as another surface?

A member on the forum recommended the following method, however my inexperience with matlab means that I'm not sure how to interpret the logical array and/or see it as a plotted surface.

>> x = [-10:10];
>> y = [-10:10];
>> test1 = x + 0.5*y;
>> test2 = x + y;
>> test3 = x + 1.5*y;
>> testI = meshgrid(test1);
>> testII = meshgrid(test2);
>> testIII = meshgrid(test3);
>> surf(x,y,testI);
>> hold on
>> surf(x,y,testII);
>> surf(x,y,testIII);
*>> OfInterest = any(diff( sort( cat(3, test1, test2, test3), 3), 3) > 0.5, 3);*
>> OfInterest
OfInterest =
    Columns 1 through 15
       0     0     0     0     0     0     0     0     1     1     0     0     0     0     0
    Columns 16 through 18
       0     0     0
>> image(OfInterest);
>> colormap(gray(2));

Thanks

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Star Strider il 18 Apr 2014

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Modificato: Star Strider il 18 Apr 2014

Does this do what you want?

x = -10:10;
[X,Y] = meshgrid(x);
test1 = X + 0.5.*Y;
test2 = X + Y;
test3 = X + 1.5.*Y;
figure(1)
surfc(X,Y,test1)
hold on
surf(X,Y,test2)
surf(X,Y,test3)
hold off
% ‘OfInterest’ -> Walter Roberson (http://www.mathworks.com/matlabcentral/answers/125901-how-to-find-when-a-surface-deviates-from-other-surface-s)
OfInterest = any(diff( sort( cat(3, test1, test2, test3), 3), 3) > 0.5, 3);
D = zeros(size(X));
D(1:size(OfInterest,1), 1:size(OfInterest,2)) = OfInterest(1:end,1:end);
figure(2)
surfc(X, Y, D)

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A il 19 Apr 2014

So would there be a way to ask MatLab to please print or give [x,y] wherever OfInterest = 1?

Sorry I don't know enough Matlab code to do this. If this was Java, I'd say something like:

if(OfInterest = 1) { system.printout([x,y]); }

lol.

Star Strider il 19 Apr 2014

Probably the easiest way is to use the find function:

[r,c] = find(OfInterest == 1);

This will give you the row- and column-indices of the elements of OfInterest that are equal to 1. You can then use them to identify the corresponding values of X and Y.

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