Plot MarkerSize units normalized

Hello! I need to plot a lot of circle of a precise size every small time-step. I was using a for with plot rcos-rsin, but it was very slow. Then I tried scatter that was very faster, but finally I used plot with 'o' parameter and MarkerSize set, that is absolutely the fastest solution. The only problem I have is the size of the marker, that never matches with what I suppose to. I tried changing 'units' to 'normalized' to both gca and gcf, but it doesn't seem to affect the MarkerSize option.

So, how do I get MarkerSize proportional to axes? Thank you.

Answer 1

[Walter Roberson]

Sorry, the MarkerSize is always in points.

curunits = get(gca, 'Units');
set(gca, 'Units', 'Points');
cursize = get(gca, 'Position');
set(gca, 'Units', curunits);

Now cursize(3) is the width in points and cursize(4) is the height in points. You can then calculate an appropriate marker size as a fraction of the axes size. If you want to catch changes in the axes size, hook into the figure ResizeFcn callback.

[Alessandro Masullo]

Thank you!

Answer 2

[Kelly Kearney]

How were you calling the circle-equation version? And how many objects are you plotting?

I ran a quick test:

ncirc = 10;
npt = 20; % # of points defining each circle

x = rand(ncirc,1)*10;
y = rand(ncirc,1)*10;
r = rand(ncirc,1)*2;

theta = linspace(0, 2*pi, 20);

xc = bsxfun(@plus, x, bsxfun(@times, r, cos(theta)));
yc = bsxfun(@plus, y, bsxfun(@times, r, sin(theta)));

figure;
hold on;
t(1) = timeit(@() scatter(x,y,r*200,'b')); % Just an example... not scaled
t(2) = timeit(@() plot(xc', yc'));

With ncirc = 10:

t =

     0.016969     0.061804

And with ncirc = 1000:

t =

      0.11602     0.061678

To adjust marker size using plot, you're going to have to create separate graphics objects for each individually-sized marker, so I doubt you would gain a ton of speed.

[Alessandro Masullo]

I've never used timeit, but this simple example shows what I mean:

x = rand(10000,1);
y = rand(10000,1);
tic, plot(x,y,'o','MarkerSize',10),toc
Elapsed time is 0.005976 seconds.
tic, scatter(x,y,10),toc
Elapsed time is 0.102514 seconds.