MATLAB Simple Point Plots

Question

In a while loop, I need to plot the positions (x,y) of two entities. That is, all I need to do is generate a plot with two points on it. I need to scale the plot to a specific maximum x and y value. An additional requirement is the fact that one of the points needs to have three concentric rings placed around it, each with a given radius. Additionally, this all is to happen in a loop, thus I'm hoping that only a single plot window opens and that I don't get a whole slew of windows opening (one for each loop iteration).

Basically here's the pseudo-code I'm trying (and failing!) to implement:

-> Open new plot window, with a given x and y axis
while (running) {
  -> Clear the plot, so figure is nice and clean
  -> Plot the two points
  -> Plot the three circles around point A
}

I found several items in MATLAB's documentation, but no single plotting functions seems to do what I want, or there are instances where I inadvertently create multiple plots with only some of the data (i.e., one plot has the points and another has the circles).

Answer 1

here's a sample code you can use in your while loop

x0=1; y0=4; 
x1=2; y1=3;  % the x-y points
r=[1 2 3]; % 3 radii of concentrating rings
ang=0:0.01:2*pi; 
xc=cos(ang)'*r;
yc=sin(ang)'*r;

plot(x0,y0,'.',x1,y1,'.'); % plot the point A
hold on
plot(x1+xc,y1+yc); % plot the 3 circles

% set the limits of the plots (though Matlab does it for you already)
xlim([min([x0 x1])-max(r) max([x0 x1])+max(r)]);
ylim([min([y0 y1])-max(r) max([y0 y1])+max(r)]);

hold off

you can make this work in a loop quite easily, read matlab's documentation on how to do that.

Answer 2

Try something like this:

r = [0.25 0.125 0.0625];
d = (1:360) / 180 * pi;
xy_circle = [cos(d)' sin(d)'];
xy_circle_1 = r(1) * xy_circle;
xy_circle_2 = r(2) * xy_circle;
xy_circle_3 = r(3) * xy_circle;

h_plot = plot(0, 0, '.k');
hold on
h_circle_1 = plot(xy_circle_1(:, 1), xy_circle_1(:, 2), '-b');
h_circle_2 = plot(xy_circle_2(:, 1), xy_circle_2(:, 2), '-r');
h_circle_3 = plot(xy_circle_3(:, 1), xy_circle_3(:, 2), '-g');
axis equal

for hh = 1:100
  xy = rand(2, 2) / 4 + 0.375;
  xlim = [0 1];
  ylim = [0 1];
  set(h_plot, 'XData', xy(:, 1));
  set(h_plot, 'YData', xy(:, 2));

  set(gca, 'XLim', xlim)
  set(gca, 'YLim', ylim)

  set(h_circle_1, 'XData', xy_circle_1(:, 1) + xy(1, 1));
  set(h_circle_1, 'YData', xy_circle_1(:, 2) + xy(1, 2));
  set(h_circle_2, 'XData', xy_circle_2(:, 1) + xy(1, 1));
  set(h_circle_2, 'YData', xy_circle_2(:, 2) + xy(1, 2));
  set(h_circle_3, 'XData', xy_circle_3(:, 1) + xy(1, 1));
  set(h_circle_3, 'YData', xy_circle_3(:, 2) + xy(1, 2));

  pause(1)
end

You can change the parameters as you wish.