How to use plot3 function inside Matlab function block used in Simulink ?

I am using Simulink to model my system. I want to visualise my model in a 3D plot. I see people generally transport data from Simulink to Matlab to visualise. Is it possible to use inbuilt Matlab functions like plot3 to visualise the system in Simulink environment ?

[VIGNESH BALAJI]

I saw that plot3 function can be used as an extern function in this case. I am trying to look into the specifics.

Answer 1

[Tejas]

Hello Vignesh,

To use the ‘plot3’ function within a MATLAB Function block in Simulink, it must first be declared as an ‘extrinsic’ function. This informs the code generator to bypass generating code for these functions and instead use the MATLAB engine to execute them. For more details on extrinsic functions, refer to this documentation: https://www.mathworks.com/help/releases/R2021b/coder/ref/coder.extrinsic.html

Additionally, other functions used alongside ‘plot3’, such as ‘hold’, ‘grid’, ‘xlabel’, ‘ylabel’, ‘zlabel’, and ‘title’, should also be declared as ’extrinsic’.

Here are the steps to use the ‘plot3’ function within a MATLAB Function block in Simulink:

• Declare ‘plot3’ and the other necessary functions as ‘extrinsic’.
• Declare a ‘persistent’ variable to refer to the figure. This ensures that each simulation of the model uses the same figure, preventing the creation of different figures for each simulation. More information on ‘persistent’ variables can be found in this documentation: https://www.mathworks.com/help/releases/R2021b/matlab/ref/persistent.html
• Use the ‘hold’ function so that the signal data from each time step accumulates on the plot instead of overwriting the previous data.

Below is an example code snippet illustrating these steps:

function plot3D(x, y, z) 
    % Specify the functions to be run in MATLAB 
    coder.extrinsic('plot3'); 
    coder.extrinsic('hold'); 
    coder.extrinsic('grid'); 
    coder.extrinsic('xlabel'); 
    coder.extrinsic('ylabel'); 
    coder.extrinsic('zlabel'); 
    coder.extrinsic('title'); 
    
    persistent h; 
    if isempty(h) 
        h = figure('Name', '3D Plot', 'NumberTitle', 'off'); 
    end 
    
    % Plot the data 
    figure(h);  
    plot3(x, y, z, 'b.-');  
    hold on; % Keep the plot for subsequent data 
    grid on;  
    xlabel('X-axis'); 
    ylabel('Y-axis'); 
    zlabel('Z-axis'); 
    title('3D Trajectory'); 
end 

Here is a screenshot of the result from an example model, showing the expected output: