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

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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

Answers (1)

DGM
DGM on 25 Sep 2024
Edited: DGM on 25 Sep 2024
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
  5 Comments
DGM
DGM on 26 Sep 2024
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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