# how to write a shapefile from the array resulted from "bwboundaries"

15 次查看（过去 30 天）
Shaohui 2023-1-13

Hi! I am a new user of Matlab and not very skilled with the syntax yet, so sorry if it sounds silly...
I would like to extract the boundaries of an image and export it as a shapefile for example.
I successfully plotted the boundaries following the tutorial (https://se.mathworks.com/help/images/boundary-tracing-in-images.html) but don't know how to write this cell object (boundaries) as a shapefile. Can I please use some help here? Thanks!
imshow(im);
BW = im2bw(im);
imshow(BW);
dim = size(BW);
col = round(dim(2)/2)-90;
row = min(find(BW(:,col)));
% To trace the boundaries of all the coins in the image, use the bwboundaries function.
BW_filled = imfill(BW,'holes');
boundaries = bwboundaries(BW_filled);
% Display the original grayscale image and use the coordinates returned by bwtraceboundary to plot the border on the image.
imshow(im)
hold on;
for k=1:length(boundaries)
b = boundaries{k};
plot(b(:,2),b(:,1),'g','LineWidth',3);
end

### 回答（1 个）

Suman Sahu 2023-3-10
Hi Shaohui,
You have extracted the boundaries of the image and stored them in the “boundaries” cell array. In order to write the cell array into a Shapefile, the cell array first needs to be converted into a geospatial structure (geo struct). A geo struct is essentially a MATLAB struct that contains specific fields related to geographic information, such as Geometry, X, Y, and so on. To learn more about geographic data structures, refer to this documentation: Geographic Data Structures - MATLAB & Simulink - MathWorks
To write the Geo struct into a Shapefile, you can use a function shapewrite, below is the syntax for that:
shapewrite(geo_struct_obj, '<shapefilename.shp>');
The following code should help you in writing the boundaries cell array into a shapefile.
imshow(im);
BW = im2bw(im);
imshow(BW);
dim = size(BW);
col = round(dim(2)/2)-90;
row = min(find(BW(:,col)));
% To trace the boundaries of all the coins in the image, use the bwboundaries function.
BW_filled = imfill(BW,'holes');
boundaries = bwboundaries(BW_filled);
% Display the original grayscale image and use the coordinates returned by bwtraceboundary to plot the border on the image.
imshow(im)
hold on;
for k=1:length(boundaries)
b = boundaries{k};
plot(b(:,2),b(:,1),'g','LineWidth',3);
end
%Extract the x and y coordinates of the boundary points into vectors
column1=[]
column2=[]
l=length(boundaries)
for i=1:l
column1=[column1; boundaries{i}(:,1)];
column2=[column2; boundaries{i}(:,2)];
end
column1=column1';
column2=column2';
%Create a struct
Boundaries_struct = struct();
Boundaries_struct.Geometry = 'MultiPoint';
Boundaries_struct.X = column1;
Boundaries_struct.Y = column2;
%Geometry, X and Y are required fields, you can add more fields to store any necessary data.
%write the struct into the shapefile
shapewrite(Boundaries_struct, 'boundaries_shapefile.shp');

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