how to generate correct logical mask of the size of shape file?

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kuldeep
kuldeep 2024-9-25
评论： kuldeep 2024-9-26
i am using following code to generate logical mask
function croppedimg = cropimage(data, R, shapefile)
% Load the shapefile and retrieve its info
S = shaperead(shapefile);
% Shapefile projections
info = shapeinfo(shapefile);
crs = info.CoordinateReferenceSystem;
[S.lon,S.lat] = projinv(crs,S.X,S.Y);
% read and reproject image file
p = R.ProjectedCRS;
[x,y] = worldGrid(R);
[lon,lat] = projinv(p,x,y);
% Create a logical mask
% Approach 1: Using 'inpolygon' function
xq = lon(:);
yq = lat(:);
in = inpolygon(xq,yq,S.lon,S.lat);
logical_mask = reshape(in,size(lon));
% Debugging: Display the logical mask summary
disp(['Total number of pixels inside polygon: ', num2str(numel(logical_mask))]);
disp(['Total number of pixels inside image: ', num2str(numel(data))]);
However it is showing the
Total number of pixels inside polygon: 16982229
Total number of pixels inside image: 16982229
please suggest me how to create correct logical mask of the size of shape file.
kuldeep

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回答（1 个）

DGM
DGM 2024-9-25
编辑：DGM 2024-9-25
Ran in:
I don't have everything to run your example, but the last lines are a problem at the least.a
Use numel() to return the total number of elements regardless of their value.
Use nnz() if you want the number of true elements in a logical array.
A = magic(5);
mask = A>15
mask = 5x5 logical array
1 1 0 0 0 1 0 0 0 1 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0
numel(mask)
ans = 25
nnz(mask)
ans = 10
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DGM
DGM 2024-9-26
If you're trying to crop out blobs from a logical mask, then you can use the 'Image' property from regionprops(), or you can use the 'BoundingBox' property and pass it to imcrop() instead.
That said, there's obviously something wrong because none of your query points are in the polygon. Without the inputs to this code, it's not apparent why that is.

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