MATLAB: Rotating N-D matrices

degreematrixrepmatrotation

hey everyone i have 2d matrix which i have repeated 24 time using repmat function. i need to rotate each of these repeated matrices by 7.5degrees. ie 1st matrix rotated 0deg, 2nd matrix rotated 7.5deg, third matrix rotated 15deg and so on… any suggestions?

Best Answer

Use a for-loop over the pages and imrotate

Something like:

X = your_original_2d_image
Xrot = zeros([size(X) 24],'like',X);
for ii = 1:24
   Xrot(:,:,ii) = imrotate(X,7.5*ii,'crop')
end

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MATLAB: N-D matrix accumarray

Yes, accumarray will do it easily. You just need to generate the correct subscripts for it, which is the cartesian product of all the indices in all the dimension, replacing the appropriate dimensions with your grouping variables:

A = randi(100, [3 4 2 7]);  %demo data
%generate indices in all the dimension, and replace appropriate one with grouping variables:
indices = arrayfun(@(s) 1:s, size(A), 'UniformOutput', false); %vector of indices in each dimension
indices{2} = [2 1 2 3];  %grouping in 2nd dimension
indices{4} = [3 3 2 1 3 2 4];  %grouping in 4th dimension
%calculate cartesian product of indices
[indices{:}] = ndgrid(indices{:});
indices = cell2mat(cellfun(@(v) v(:), indices, 'UniformOutput', false));
%apply accumarray with default sum function
B = accumarray(indices, A(:));

Edit: note that the above will work with arrays of any dimension (within reason, ndgrid will run out of memory for too many dimensions).

MATLAB: Help with rotation any single matrix of 3D matrix by 90 degrees

A = rand(5,4,3);
A1=rot90(A(:,:,1))          %first page matrix rotated 90 degrees
A1(1,:)=rand(1,size(A,1))   %first row inserted with random values

Best Answer

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MATLAB: N-D matrix accumarray

MATLAB: Help with rotation any single matrix of 3D matrix by 90 degrees

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