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

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

Answer 1

[DGM]

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

[kuldeep]

Thanks a lot for your kind help. I have modified the lines as follows

% Debugging: Display the logical mask summary

disp(['Sum of pixels inside polygon: ', num2str(nnz(logical_mask))]);

disp(['Total number of pixels inside image: ', num2str(numel(logical_mask))]);

ans it is displaying as

Sum of pixels inside polygon: 0

Total number of pixels inside image: 16982229

and the size of cropped image is [0 0]

I request you to please suggest me how to get correct correct size of cropped image.

kuldeep

[kuldeep]

i am attaching the figure of image and logical mask and request you to please have a look on it.

[Drishti]

Can you share the data files, it will be easy for us to look into it.

[DGM]

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.

[kuldeep]

Thanks for your help. I am attaching the shape file and data file.