- bwboundaries: https://www.mathworks.com/help/images/ref/bwboundaries.html
- imread: https://www.mathworks.com/help/matlab/ref/imread.html
- imbinarize: https://www.mathworks.com/help/images/ref/imbinarize.html
- reducepoly: https://www.mathworks.com/help/images/ref/reducepoly.html
- createpde: https://www.mathworks.com/help/pde/ug/createpde.html
How to make PDE geometry from the BW mask?
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Hello, I'd like to analyzed my data with temporally changed boundary shape by adapting the FEM.
Here, I already got the BW mask for the boundary, but I still don't how to change it as a geometry structure for the FEM which can put into the "geometryFromEdges" function. My BW mask data have the all the coorrdinate of x and y position as a matrix. In this case, how can I change it to the geometry feature which can fit on the geometryFromEdges ?
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Abhishek Chakram
el 24 de Abr. de 2024
Hi Hyuntae Jeong,
To adapt a BW mask representing the boundary of a domain into a geometry structure suitable for FEM analysis in MATLAB, especially for use with the “geometryFromEdges” function, you will need to convert the boundary represented by your BW mask into a set of edges or curves that describe the geometry. This process involves several steps:
1.Extract Boundary Coordinates: You can use the “bwboundaries” function to extract the boundaries from the binary mask.
BW = imread('path_to_your_mask_image.png'); % Load your BW mask
BW = imbinarize(BW); % Ensure it's binary in case it's not
boundaries = bwboundaries(BW, 'noholes');
This will give you a cell array boundaries where each cell contains the (x, y) coordinates of a boundary. If your mask has one main object, you can focus on the first cell.
2. Simplify Boundary: Simplify the extracted boundary to reduce the number of points while maintaining the shape. You can use “reducepoly” function for the same.
boundary = boundaries{1}; % Assuming one main boundary
simplifiedBoundary = reducepoly(boundary, tolerance); % Set 'tolerance' appropriately
3. Create Geometry Definition: Once you have the simplified boundary, you need to create a set of edges that can be used with “geometryFromEdges”. In MATLAB, this often involves defining the boundary using lines, circles, and other shapes programmatically. For a custom shape, you might need to interpolate the boundary points into a spline or a set of line segments that approximate the boundary well. Here is how you might approach it with line segments:
% Example: Creating a custom geometry function for a simple shape
function [sf, name] = customGeometry(simplifiedBoundary)
% Assuming simplifiedBoundary is an Nx2 matrix of (x,y) points
% Create line segments between consecutive points
str = [];
for i = 1:size(simplifiedBoundary, 1)-1
str = [str, 'L', '(' num2str(simplifiedBoundary(i,1)), ',', num2str(simplifiedBoundary(i,2)), ')', '-', ...
'(' num2str(simplifiedBoundary(i+1,1)), ',', num2str(simplifiedBoundary(i+1,2)), ')'];
if i < size(simplifiedBoundary, 1)-1
str = [str, '+'];
end
end
sf = str;
name = 'customBoundary';
end
Then, use your custom geometry in the PDE model:
model = createpde();
[sf, name] = customGeometry(simplifiedBoundary);
geometryFromEdges(model, @(x) eval(name));
You can refer to the following documentation to know more about functions used:
Best Regards,
Abhishek Chakram
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