demo07 of Im2mesh package

demo07 - Function plotMeshes
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
Jiexian Ma, mjx0799@gmail.com Project website List of demo
Table of Contents
Note Initialize Overview Import image Generate mesh Select colormap Set display mode Other settings Highlight low quality elements

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. No need to install any MATLAB toolboxes when running this demo.

Initialize

Before we start, please set folder "Im2mesh_Matlab" as your current folder of MATLAB.
clearvars
Set default image size (optional).
x = 250; y = 250; width = 300; height = 300;
set(groot, 'DefaultFigurePosition', [x,y,width,height])
% To reset:
% set(groot, 'DefaultFigurePosition', 'factory')
Function im2mesh use a mesh generator called MESH2D (developed by Darren Engwirda). We can use the following command to add the folder 'mesh2d-master' to the path of MATLAB.
addpath(genpath('mesh2d-master'))

Overview

We will demostrate function plotMeshes in this demo.
There are 4 typical usage of function plotMeshes
% usage 1:
% plotMeshes( vert, ele );
%
% usage 2:
% plotMeshes( vert, ele, tnum );
%
% usage 3:
% plotMeshes( vert, ele, tnum, color );
%
% usage 4:
% plotMeshes( vert,ele,tnum, color, opt )
The meanings of the input arguments are as follows:
color: Color code for selecting colormap. Interger. Value: 0-10. Default value: 0
0: grayscale, 1: lines, 2: parula, 3: turbo, 4: jet, 5: hot, 6: cool, 7: summer, 8: winter, 9: bone, 10: pink.
opt: a structure array. It is the extra options for plotMeshes. It stores extra parameter settings for plotMeshes.
opt.mode: display mode. Value: 1 or 2.
opt.wid: line width of the plotted edges. Default value: 0.5
opt.alpha: edge line transparency. It's a scalar value in range [0,1]. Default value: 0.5
opt.beta: brightness adjustment of colormap. [-1, 1]. Default value: 0
opt.tf_gs: Boolean value. Whether to use graphics smoothing when plotting. Default value: 1
opt.q_thresh: threshold for mesh quality. Those elements with mesh quality lower than opt.q_thresh will be highlighted. Default value: 0

Import image

im = imread('logo.tif');
if size(im,3) == 3; im = rgb2gray( im ); end
imshow( im,'InitialMagnification','fit' );

Generate mesh

opt = []; % reset
opt.tolerance = 1;
opt.grad_limit = 0.2;
[ vert, tria, tnum, vert2, tria2 ] = im2mesh( im, opt );
Refine triangulation... ------------------------------------------------------- |ITER.| |CDT1(X)| |CDT2(X)| ------------------------------------------------------- 9 128 110 10 128 223 17 163 449 Refine triangulation... ------------------------------------------------------- |ITER.| |CDT1(X)| |CDT2(X)| ------------------------------------------------------- 10 275 110 18 299 110 20 307 855 30 324 2209 33 324 2215 Smooth triangulation... ------------------------------------------------------- |ITER.| |MOVE(X)| |DTRI(X)| ------------------------------------------------------- 10 64 2193
Plot mesh
plotMeshes( vert, tria, tnum )

Select colormap

color = 2;
plotMeshes( vert,tria,tnum, color )

Set display mode

When opt.mode=1, plot faces and edges. Slower.
When opt.mode=2, plot edges only. Faster.
Default value: 1
color = 2;
opt = []; % reset
opt.mode = 2;
plotMeshes( vert,tria,tnum, color, opt )

Other settings

When the mesh data is huge, I usually set 'opt.alpha' to 0.2-0.3.
color = 2;
opt = []; % reset
opt.mode = 2;
opt.wid = 0.5;
opt.alpha = 0.3;
opt.beta = 0.5;
plotMeshes( vert,tria,tnum, color, opt )

Highlight low quality elements

Those elements with mesh quality lower than 'opt.q_thresh' will be highlighted.
You can set color to 0 to faciliate the visualization.
color = 0;
opt = []; % reset
opt.mode = 1;
opt.wid = 0.5;
opt.alpha = 0.2;
opt.beta = 0;
opt.q_thresh = 0.6;
plotMeshes( vert,tria,tnum, color, opt )
% reset image size
set(groot, 'DefaultFigurePosition', 'factory')
% end of demo