Combine Two polyshape Objects Similar to addCell Functionality

Hello everyone,

I am working with polyshape objects in MATLAB and want to combine (a bigger and a smaller) two polygons into one. I create a rectangular domain as the first polygon (p1) and a sawtooth-based shape as the second polygon (p2). My goal is combine these polygons, but obtain one polygon with two NumRegions, similar to the functionality of an addCell function (only 3D).

I know it is possible to generate the desired shape in a different way (but using only square, circles, etc). However, I am specifically using polyshape because I need to create custom shapes.

Here’s the code I’m using:

close all; clear; clc;

% First polygon 
Lx = 40; % Length of the rectangular domain [mm]
Ly = 20; % Height of the rectangular domain [mm]
p1 = polyshape([0, Lx, Lx, 0], [Ly, Ly, 0, 0]); % Rectangular domain

% Second polygon
T = 10 * (1 / 50); 
fs = 1000; 
t = 0:1/fs:T-1/fs; 
fun = sawtooth(2 * pi * 50 * t); 
ini_tickness = 1 * ones(size(fun)); 
in_Domain = ini_tickness + normalize(fun, "range"); 


x_holo = linspace(0, Ly - 1, length(in_Domain)); 
y_holo = in_Domain; 

p2 = polyshape([x_holo, fliplr(x_holo)], [zeros(size(x_holo)), fliplr(y_holo)]);

Warning: Polyshape has duplicate vertices, intersections, or other inconsistencies that may produce inaccurate or unexpected results. Input data has been modified to create a well-defined polyshape.

p2 = rotate(p2, -90, [20, 0]); % Rotate
p2 = translate(p2, -19, -0.5); % translate

%Showing

figure(1);
subplot(2,1,1)
plot(p1);
axis equal;
subplot(2,1,2)
plot(p2);
axis equal;

pt=subtract(p1,p2);
figure(2);
plot(pt);

disp(['NumRegions:' num2str(pt.NumRegions)])

NumRegions:1

Answer 1

[Steven Lord]

p1 = nsidedpoly(4);
p2 = nsidedpoly(5);

The union function makes a polyshape with 1 region.

P = union(p1, p2)

P = 
  polyshape with properties:

      Vertices: [17x2 double]
    NumRegions: 1
      NumHoles: 0

Concatenation makes an array of polyshapes.

P2 = [p1, p2]

P2 = 
  1x2 polyshape array with properties:

    Vertices
    NumRegions
    NumHoles

figure;
plot(p1);
axis([-1.5 1.5 -1.5 1.5]) % Make all the axes limits the same for visual comparison
title('square')

figure
plot(p2)
axis([-1.5 1.5 -1.5 1.5]) % Make all the axes limits the same for visual comparison
title('pentagon')

figure
plot(P)
axis([-1.5 1.5 -1.5 1.5]) % Make all the axes limits the same for visual comparison
title('union of a square and a pentagon')

figure
plot(P2)
axis([-1.5 1.5 -1.5 1.5]) % Make all the axes limits the same for visual comparison
title('two polyshapes, a square and a pentagon')

Note the differences in color in the plots of P and P2.

[Darby Paez]

Hi, thank you for your answer. However, that's not exactly what I was asking. Using union, the result is a single polygon with one NumRegions, and with concat ([]), they are treated as two polygons.

What I actually need is a single polyshape object with two NumRegions or Face, as I intend to use it to define subdomains. Additionally, as I mentioned earlier, I am using polyshape because I need to create custom shapes. Something I tried was using "subtranct" and addFaces to the result, but it was not possible.