demo02 of Im2mesh package
demo02 - Demonstrate function im2meshBuiltIn, which use matlab built-in function generateMesh as mesh generator.
Cite as: Ma, J., & Li, Y. (2025). Im2mesh: A MATLAB/Octave package for generating finite element mesh based on 2D multi-phase image (2.1.5). Zenodo. https://doi.org/10.5281/zenodo.14847059
Table of Contents
Note
I suggest familiarizing yourself with Im2mesh_GUI before learning Im2mesh package. With graphical user interface, Im2mesh_GUI will help you better understand the workflow and parameters of Im2mesh package.
Im2mesh_GUI: https://www.mathworks.com/matlabcentral/fileexchange/179684-im2mesh_gui-2d-image-to-finite-element-mesh
If you are using Im2mesh package in MATLAB, you need to install MATLAB Image Processing Toolbox and Mapping Toolbox because Im2mesh package use a few functions in these toolboxes.
Setup
Before we start, please set folder "Im2mesh_Matlab" as your current folder of MATLAB.
clearvars
Set default image size.
x = 250; y = 250; width = 250; height = 250;
set(groot, 'DefaultFigurePosition', [x,y,width,height])
% To reset:
% set(groot, 'DefaultFigurePosition', 'factory')
Add the folder 'mesh2d-master' to the path of MATLAB.
addpath(genpath('mesh2d-master'))
To use function im2meshBuiltIn, you need to install MATLAB Partial Differential Equation Toolbox.
Kumamon
Let's start demo02. We'll demostate the usage of function im2meshBuiltIn.
Import image kumamon.tif.
im = imread('kumamon.tif');
if size(im,3) == 3; im = rgb2gray( im ); end
imshow( im,'InitialMagnification','fit' );
Let's use function im2meshBuiltIn to generate meshes based on the kumamon image. We will use default settings. Note that function im2meshBuiltIn is quite similar to function im2mesh. Just the mesh generator is different. Function im2meshBuiltIn use matlab built-in function generateMesh (https://www.mathworks.com/help/pde/ug/pde.pdemodel.generatemesh.html) as mesh generator.
[ vert, tria, tnum ] = im2meshBuiltIn( im );
plotMeshes( vert, tria, tnum )
We can get the mean value of Q.
mean(triscr2( vert, tria ))
ans = 0.9509
Wonderful! Let's check the total number of triangles in the mesh.
size( tria, 1 )
ans = 1454
Parameters of function im2meshBuiltIn
There're two ways to call function im2meshBuiltIn.
[ vert, tria, tnum ] = im2meshBuiltIn( im ); % this use default opt setting
[ vert, tria, tnum ] = im2meshBuiltIn( im, opt );
Variable opt means options. It's a structure array used to stored input parameters for function. We can take a look at the default value of opt.
% opt is a structure array for parameters
opt.tf_avoid_sharp_corner = false;
opt.lambda = 0.5;
opt.mu = -0.5;
opt.iters = 100;
opt.threshold_num_turning = 10;
opt.threshold_num_vert_Smo = 10;
opt.tolerance = 0.3;
opt.threshold_num_vert_Sim = 10;
opt.hgrad = 1.25;
opt.hmax = 500;
opt.hmin = 1;
opt.select_phase = [];
The meaning of these parameters are listed the file "Im2mesh functions and parameters.pdf". Please refer to "Im2mesh_GUI Tutorial.pdf" about how to choose the value of these parameters. You can change these default values by editting function setOption in "im2meshBuiltIn.m".
Quadratic element
Function im2meshBuiltIn can also generate quadratic element via the following syntax.
[ vert, tria, tnum, vert2, tria2 ] = im2meshBuiltIn( im ); % this use default opt setting
[ vert, tria, tnum, vert2, tria2 ] = im2meshBuiltIn( im, opt );
Ouput variables - vert, tria, tnum define linear elements.
Ouput variables - vert2, tria2, tnum define quadratic elements.
Their meanings have been listed in demo01.
Example 1
Let's show some examples with different opt.
% example 1
opt = []; % reset opt
opt.tolerance = 0.2;
opt.hmin = 0.1; % Min Mesh Edge Length
[ vert, tria, tnum ] = im2meshBuiltIn( im, opt );
plotMeshes( vert, tria, tnum );
Example 2
% example 2
opt = []; % reset opt
opt.tolerance = 0.2;
opt.hmin = 5; % Min Mesh Edge Length
[ vert, tria, tnum ] = im2meshBuiltIn( im, opt );
plotMeshes( vert, tria, tnum );
% reset image size
set(groot, 'DefaultFigurePosition', 'factory')
% end of demo