Randomly generated complex polygon with user input

I want to generate a randomly shaped complex polygon which has start point (0,0) and has vertices defined by user input.

Answer 1

[Image Analyst]

How about using ginput() or impoly()?

[Matthew]

No i need the function to draw the polygon not the user the user just supplies the number of vertices.

[Image Analyst]

Use inputdlg() to get an integer. Then

coordinates = rand(numberOfVertices, 2);
coordinates(1,:) = [0, 0]; % Force first coord to 0,0
plot(coordinates(:,1), coordinates(:,2), 'r-');

Note - it's very "complex" = it can even have overlapping regions (figure 8's). If you don't want that, you have to find the average (centroid) and find all the angles, and sort by angle. At least that's one way.

[Matthew]

I tried but i just got this error.

Undefined function or variable 'numberOfVertices'.

Error in plotfunc (line 3) coordinates = rand(numberOfVertices, 2);

prompt = {'Enter Number of verticies:'};
numberOfVerticies = inputdlg(prompt);
coordinates = rand(numberOfVertices, 2);
coordinates(1,:) = [0, 0]; % Force first coord to 0,0
plot(coordinates(:,1), coordinates(:,2), 'r-');

[Image Analyst]

Sorry - misspelled it. Try this:

prompt = {'Enter Number of vertices:'};
numberOfVertices = str2num(cell2mat(inputdlg(prompt, 'enter a number', 5)))
coordinates = rand(numberOfVertices, 2);
coordinates(1,:) = [0, 0]; % Force first coord to 0,0
coordinates(end+1,:) = [0, 0]; % Force last coord to 0,0
plot(coordinates(:,1), coordinates(:,2), 'bo-');
grid on;

[Matthew]

Exactly what i need thank you for the help. One last thing, is there an easy way to fill the plot with a colour?

[Image Analyst]

Try patch() or fill().

[Matthew]

i tried both i just cant get them to work. No way of typing fill works i'm stuck on it. I want it to use 'RGB::random()' for the color so all would be different.

function plotfunc()

prompt = {'Enter Number of vertices:',}
numberOfVertices = str2num(cell2mat(inputdlg(prompt, 'enter a number', 5)))
coordinates = rand(numberOfVertices, 2);
coordinates(1,:) = [0, 0]; % Force first coord to 0,0
coordinates(end+1,:) = [0, 0]; % Force last coord to 0,0
plot(coordinates(:,1), coordinates(:,2));
fill(plot(coordinates(:,1), coordinates(:,2)),'RGB::random()');
grid on;

end

[Matthew]

Is it just me getting the fill(X,Y,C) wrong?

[Image Analyst]

You can't put plot() inside fill(). Take it out. Try this:

% prompt = {'Enter Number of vertices:',}
% numberOfVertices = str2num(cell2mat(inputdlg(prompt, 'enter a number', 5)))
numberOfVertices = 7; % Fixed at 7 for this demo.
coordinates = rand(numberOfVertices, 2);
coordinates(1,:) = [0, 0]; % Force first coord to 0,0
coordinates(end+1,:) = [0, 0]; % Force last coord to 0,0
plot(coordinates(:,1), coordinates(:,2));
grid on;
patch(coordinates(:,1), coordinates(:,2),'r'); % Can use fill() also.
grid on;

[Matthew]

Yep that works :) but I can't get the 'RGB::random()' to work as I want it to make a random colour each time.

[Image Analyst]

Where did you see 'RGB::random()' ? I don't see it in the help as one of the 'ColorSpec' types.

[Matthew]

It was on a google search result for matlab random colours.

[Image Analyst]

If it ever was allowed, it's not now, not that I can find. See the help. You can use

fill(x, y, 'Color', rand());

if you want a random color.

[Matthew]

For some reason this keeps giving me green.

patch(coordinates(:,1), coordinates(:,2),rand());

[Image Analyst]

Sorry, you need 3 numbers. Try this:

randomColor = rand(1,3)
patch(coordinates(:,1), coordinates(:,2), randomColor); % Can use fill() also.

[Matthew]

YES! it works :) thank you. Now I just have to flip it in the x and y axis.

[Image Analyst]

There is an 'xdir' property where you can reverse the direction. I think it's something like

set(gca, 'xdir', 'reverse');

or something like that. If this is solved, then mark the answer as "Accepted."