Is it possible to insert a polyshape onto an already defined grid?

Hi,

If i already have a 10x10 grid (say ranging from 1:10 in both x and y) and I create a triangle (lets say a side length of 2) using polyshape (or other) is there a way to impose the triangle onto the already preestablished grid? The aim is to have a grid where I can place objects and have greater ability of manipulating them such as rotating them.

Currently im using loops to make the triangle on the pre-established grid, but I have no control of its rotation.

If there is a better way of going about this then please let me know!

Answer 1

[VINAYAK LUHA]

Hi Johnny,

I understand that you want to insert a polyshape onto a preestablished grid in MATLAB and further you also want to manipulate the shape's position and orientation in the grid.

Follow the below steps to plot a triangle using the "polyshape" function in a grid and manipulate its position and orientation using arrow keys.

1. Create a grid using the "meshgrid" function.
2. Define the vertices of the triangle and create a polyshape of the triangle providing the vertices of the triangle as input to the "polyshape" function.
3. Create a figure and plot the defined grid and triangle.
4. Attach a callback function to the created figure, say "KeyPressFcn" to capture key press events on the figure.
5. Implement the "KeyPressFcn" such that -

• It identifies the key presses and configures the corresponding action to perform.
• An Action takes the current polyshape object as input and modifies its vertices as per pre-defined transformation.
• Clear the current figure and replot the modified polyshape to it.

Here is the detailed code snippet to implement the above instructions-

global x;
global y;
[x, y] = meshgrid(1:10, 1:10);
triangleVertices = [3 3; 5 3; 4 5]; 
global triangle
triangle = polyshape(triangleVertices);
figure;
plot(x, y, 'k.');
hold on;
plot(triangle); 
set(gcf, 'KeyPressFcn', @keyPressed);
function keyPressed(~, event)
    global triangle 
    step = 0.1;
    switch event.Key
        case 'uparrow'
            triangle = translate(triangle, [0, step]); 
        case 'downarrow'
            triangle = translate(triangle, [0, -step]); 
        case 'leftarrow'
            triangle = rotate(triangle, deg2rad(20), mean(triangle.Vertices)); 
        case 'rightarrow'
            triangle = rotate(triangle, deg2rad(-20), mean(triangle.Vertices));
    end
   
    clf;
    global x;
    global y;
    plot(x, y, 'k.'); 
    hold on;
    plot(triangle); 
end

Additionally, refer to the following documentations for more details on how to use the above-mentioned functions-

• meshgrid function
• https://www.mathworks.com/help/matlab/ref/meshgrid.html
• polyshape function
• https://www.mathworks.com/help/matlab/ref/polyshape.html
• matrix-representation-of-geometric-transformations
• https://www.mathworks.com/help/images/matrix-representation-of-geometric-transformations.html
• create-callbacks-for-graphics-objects
• https://www.mathworks.com/help/matlab/creating_plots/create-callbacks-for-graphics-objects.html

Hope this helps you in understanding how to insert a polyshape onto a pre-established grid in MATLAB and further manipulate its position and orientation.

Best regards,

Vinayak Luha