how to slice a 3d array with slider?

Question

Rabih Sokhen 2022-6-19

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1743335-how-to-slice-a-3d-array-with-slider

评论： Voss 2022-6-19

Code:

clear all
clc
y=randn(10,10,10);
h = uicontrol('style','slider','Min',0,'Max',100,'Value',0.01, 'callback',@(src,evt)disp(get(src,'value')));
a=ceil(h.Value)
pcolor(y(:,:,a))

% i would like to move the slider along the z direction and slice my "y" at the exact position where my slider stops.

can someone help me plz

thank you in advance

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Answer 1

Voss 2022-6-19

0
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https://ww2.mathworks.cn/matlabcentral/answers/1743335-how-to-slice-a-3d-array-with-slider#answer_988560

编辑：Voss 2022-6-19

在 MATLAB Online 中打开

Here's one way to do that:

clear all
clc
y = randn(10,10,10);
N = size(y,3);
h = uicontrol( ...
    'style','slider', ...
    'Min',1, ...
    'Max',N, ...
    'Value',1, ...
    'SliderStep',[1 3]/(N-1), ...
    'Units','normalized', ...
    'Position',[0 0 1 0.06], ...
    'callback',{@cb_slice,y});
cb_slice(h,[],y); % initialize the plot
function cb_slice(src,evt,y)
pcolor(y(:,:,round(src.Value)));
end

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Rik 2022-6-19

For general advice and examples for how to create a GUI (and avoid using GUIDE), have look at this thread. You will find the advice to use explicit handles.

Voss 2022-6-19

在 MATLAB Online 中打开

@Rabih Sokhen: Notice how the slider's Callback is specified to have y as an input argument:

'callback',{@cb_slice,y}

That is done so that cb_slice has access to the variable y.

If you want cb_slice to operate on two arrays, then you can send both of them as input arguments:

'callback',{@cb_slice,y,u}

and change the definition of cb_slice to include u, and also include both calls to pcolor and both calls to subplot in there:

function cb_slice(src,evt,y,u)
subplot(121)
pcolor(y(:,:,round(src.Value)));
subplot(122)
pcolor(u(:,:,round(src.Value)));
end

and initialize the plots by calling cb_slice once with both arrays when the program starts:

cb_slice(h,[],y,u); % initialize the plots

[ Note that if the size of y and the size of u in their third dimension are not the same, then you'll have some problems. Specifically, if size(u,3) > size(y,3), then you won't be able to see the slices of u beyond size(y,3), and if size(u,3) < size(y,3), then you'll get an error trying to access slices of u that don't exist when the slider Value is greater than size(u,3). ]

Now, the slider callback is creating new pcolor surfaces in each subplot each time it is called, which is inefficient. A better way would be to create the pcolor surfaces once when the program starts, and have the slider Callback merely update them rather than creating new ones:

clear all
clc
y = randn(10,10,10);
u = randn(10,10,10);
N = size(y,3);
% create the pcolor surfaces
subplot(121)
p(1) = pcolor(y(:,:,1));
subplot(122)
p(2) = pcolor(u(:,:,1));
h = uicontrol( ...
    'style','slider', ...
    'Min',1, ...
    'Max',N, ...
    'Value',1, ...
    'SliderStep',[1 3]/(N-1), ...
    'Units','normalized', ...
    'Position',[0 0 1 0.06], ...
    'callback',{@cb_slice,p,y,u});
cb_slice(h,[],p,y,u); % initialize the plots
function cb_slice(src,evt,p,y,u)
val = round(src.Value);
p(1).CData = y(:,:,val);
p(2).CData = u(:,:,val);
end

As you can see there, now cb_slice has another additional input argument, p, which is an array of surfaces created by pcolor.

At this point, it's worth pointing out another approach: rather than passing everything you need as input arguments to the callback function(s), you can make cb_slice a nested function:

function pcolor_slider_test()
clc
y = randn(10,10,10);
u = randn(10,10,10);
N = size(y,3);
% create the pcolor surfaces
subplot(121)
p(1) = pcolor(y(:,:,1));
subplot(122)
p(2) = pcolor(u(:,:,1));
h = uicontrol( ...
    'style','slider', ...
    'Min',1, ...
    'Max',N, ...
    'Value',1, ...
    'SliderStep',[1 3]/(N-1), ...
    'Units','normalized', ...
    'Position',[0 0 1 0.06], ...
    'callback',@cb_slice);
cb_slice(); % initialize the plots
    function cb_slice(~,~)
        val = round(h.Value);
        p(1).CData = y(:,:,val);
        p(2).CData = u(:,:,val);
    end
end

Now p, y, and u don't have to be passed in to cb_slice because cb_slice is nested under the main function (which I call pcolor_slider_test), which means that the code inside cb_slice "sees" the variables in pcolor_slider_test's workspace, so they don't have to be given as input arguments. Using nested functions makes the code cleaner, in my opinion, and it's the approach I would probably use if I were doing this myself.

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