Draw filled triangle and possibly change aspect ratio

How can I draw a filled equilateral triangle (actually white) with background black? I don't want to have any x and y axis on the drawing. I just need the graph.

And also how can I define an aspect ratio (hight:width) of the triangle and then get the different triangles of different aspect ratio from an equilateral triangle?

I think some logic for the length of pixels should work but I could not figure out.

Thanks in adavance!!

[Rik]

You can probably solve your question with the patch function. You only need to calculate the coordinates of the corners.

Answer 1

[Payas Bahade]

Hi Chen,

As mentioned by Rik, you can use patch command to draw the triangles and set axes properties to get desired results. Below mentioned code will help you draw triangles with specified aspect ratio:

w=10; %width of triangle
ar=0.866; % Aspect ratio for equilateral triangle
h=ar*w;%height of triangle
x=[0 w w/2];%x coordinates of vertices
y=[0 0 h];%y coordinates of vertices
patch(x,y,'white') %plotting triangle in white color
set(gca,'Color','k','xticklabel',[],'yticklabel',[])%setting background black and removing labels
daspect([1 1 1]);%equal data unit length along x and y axis
xlim([-5 15])
ylim([-5 15])

You can tweak above code to get required geometry for the triangle.

Kindly refer this documentation link to know more details on using ‘patch’ command.

Hope this helps!

[Chen]

Thank you so much Payas! This is exactly what I want! I will look at the link for 'patch' command.

[Chen]

Just another question: How can I save the final output as a matrix without manually save it on the image panel? I tried to let 'p = patch(x,y,'white')' but it is not the final pop-up output. Thanks so much!

[Chen]

Another question: How to keep the triangle always in the middle of the graph? i.e., the width from the top of the output graph to the top of the triangle is equal with width of the bottom of the output graph to the bottom of the triangle.

Thanks so much!!

[Payas Bahade]

You can define the axes limits in terms of triangle's width and height to get require spacing around the triangle as follows:

% setting the axes limits 
xlim([-w/2 1.5*w])
ylim([-w/2 h+w/2])

And to save the output figure, you can use 'savefig' command as follows:

% saving the figure
output=gcf;
savefig(output,'Triangle.fig');

[Ron]

Hi Payas,

Can you help me please? I used the code above to create one triangle. How can I create randomly distributed 500 triangles of size 3.4 x 3.4 x 3 cm? Thank you.

Answer 2

[Chen]

a solution by myself:

Use the logic of the pixels' positions:

function trianglePixels = ar_t_man(i)

a = zeros(150,150);  %define graph size -- you can change 
                     % will fill the triangle by value 1 (binary)
                                       
a(20,size(a,2)/2) = 1;        %define position of the top point in the triangle  
                              % -- you can change

b = 1:i*100; %how many columns in the triangle due to aspect ratio

for j = 1:size(b,2)
a(20+b(j),floor(size(a,2)/2-(50/size(b,2)*j)):floor(size(a,2)/2+(50/size(b,2)*j))) = 1;   %the actual triangle
end

trianglePixels = a;
imshow(a, [])
end