How to subset the matrix/array with shape file?

2018 6 26
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更新时间：2020 10 22
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I have matrix of 890*751 and array 890*751*5 and I want to clip/crop/subset this matrix and array with shape file. The shape file is consist on several sub-polygon inside. Each inside sub-polygon of shape file has to clip/crop/subset separately and save with unique name. E.g, we have a shape file with 4 sub-polygon (with name (a,b,c,d) and we have to get 4 clip/crop/subset(a,b,c,d) of the matrix/array with. we can read the shape file by
area = shaperead('shapefile', 'UseGeoCoords', true);
geoshow( area , 'Facecolor', 'blue')
but no idea how to crop/clip/subset the matrix/array. The sample testmatrix, testarray and shapefile are attached here for easy to understand the question. Thank you in advance for any helpe/guide

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KSSV
KSSV 2018-6-26
YOu need to provide the lat and lons for matrices.
Shakir Hussain
Shakir Hussain 2018-6-26
Dear KSSV, the lat lon of matrix are attached here
KSSV
KSSV 2018-6-26
编辑：KSSV 2018-6-26
aaah...got it....

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KSSV
KSSV 2018-6-26
编辑：KSSV 2018-6-26

0 个投票

Check this link for a similar question. You can follow the same code.
https://in.mathworks.com/matlabcentral/answers/403555-how-to-extract-data-through-the-shapefile-india-from-global-precipitation-data
shapefile = 'shapefile.shp' ;
S = shaperead(shapefile) ;
N = length(S) ;
for i = 1:N
plot(S(i).X,S(i).Y)
hold on
end
lon = load('testlon.mat') ; lon = lon.testlon ;
lat = load('testlat.mat') ; lat = lat.testlat ;
[X,Y] = meshgrid(lon,lat) ;
data = load('testarray.mat') ; data = data.testarray ;
[nx,ny,d] = size(data) ;
%%Extract data
iwant = cell(d,N) ;
for i =1:d
A = data(:,:,i) ;
for j = 1:N
idx = inpolygon(X(:),Y(:),S(i).X,S(i).Y) ;
iwant{i,j} = A(idx) ;
end
end

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Shakir Hussain
Shakir Hussain 2018-6-28
编辑：Walter Roberson 2018-6-28
Thanks your response.
shapefile = 'AoiTp.shp';
S = shaperead(shapefile);
N = length(S);
for i = 1:N
plot(S(i).X,S(i).Y)
hold on
end
lat = testlat;
lon = testlon;
[X,Y] = meshgrid(lon,lat);
data = testarray;
[nx,ny,d] = size(data);
%%Extract data
iwant = cell(d,N);
for i =1:d
A = data(:,:,i);
for j = 1:N
idx = inpolygon(X(:),Y(:),S(i).X,S(i).Y);
iwant{i,j} = A(idx);
end
end
Why I am getting the error "Index exceeds matrix dimensions". If it work, then How we can extract the data by sub-polygon of a shape file?
Walter Roberson
Walter Roberson 2018-6-28
The number of entries in the shapefile, N, is not definitely the same as the size of the third dimension in testarray, especially if testarray turns out to be 4 dimensional.
KSSV
KSSV 2018-6-28
Which line shows error? Code worked fine with your data in my pc.
Shakir Hussain
Shakir Hussain 2018-6-28
编辑：Shakir Hussain 2018-6-28
I think Walter is right, the third line of code (N = length(S) is equal to 5 and iwant = cell(d,N); is extracting only 5 instead of 17.
Shakir Hussain
Shakir Hussain 2018-7-6
Error in ==> run at 18 idx = inpolygon(X(:),Y(:),S(i).X,S(i).Y) ;
Here is the error I am getting from the code
Shakir Hussain
Shakir Hussain 2018-8-18
Error in ==> run at 18 idx = inpolygon(X(:),Y(:),S(i).X,S(i).Y) ; Here is the error I am getting from the code ( Index exceeds array bounds)
KSSV
KSSV 2018-8-18
What is i? I think i is going beyond length(S).
Shakir Hussain
Shakir Hussain 2018-8-19
Yes, Now it is fixed and code is working well. Last thing is how we convert the result (iwant) into 2d matrix according to the polygon extend?
Adi Mulsandi
Adi Mulsandi 2020-10-22
Hi Shakir Hussain can you share how to convert the result (iwant) into 2d matrix according to the polygon extend?

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