Circular Indexing of Array

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Tyler Smith
Tyler Smith 2018-8-16
评论： Tyler Smith 2018-8-17
I have a question that has been addressed in some capacity here: https://www.mathworks.com/matlabcentral/answers/44993-circular-indexing-of-an-array. However I am not sure how to use this approach for my array. I am clustering data in a 73 x 144 array with bwlabel. However, the data should be treated as circular (rather spherical) as it is Earth Surface data. So I want to be able to apply bwlabel such that the right side of the array is technically continued into the left side of the array. I have tried appending the array such that I tack on 10 or 15 columns on both the left and right side of the array, but that generates false clusters. I have attached an image of my problem. The top center of the image (at North Pole) the pink and light blue clusters should be the same, but are separated by bwlabel since the array begins at 0 degrees longitude and ends at 360 degrees longitude. Any suggestions would be great!

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回答（1 个）

Chad Greene
Chad Greene 2018-8-16
If you have lat,lon grids corresponding to your matrix Z, try using the attached function to recenter like this:
[lat,lon,Z] = recenter(lat,lon,Z);
If your lat and lons are 1D arrays, you might need to grid them with meshgrid first by either
[lon,lat] = meshgrid(lon,lat);
or
[lat,lon] = meshgrid(lat,lon);
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Chad Greene
Chad Greene 2018-8-16
Is it prohibitive to triple the size of your dataset, like if
Z = peaks;
then tripling it would look like
Z3 = [Z Z Z];
After doing your analysis, you could get the middle section back, like
Z_analyzed = Z3(:,size(Z,1)+1:2*size(Z,1));
Tyler Smith
Tyler Smith 2018-8-17
The problem that creates is 'bwlabel' or 'labelmatrix' would then generate 3 times the number of clusters since it clusters adjacent cells. There would still be a discontinuous / improper clustering on the edge of the array after extracting the middle section.

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