get(axH,'position') reporting incorrect values?

hi all. it appears that getting an axes 'position' will sometimes report incorrect values.

here is how i produce reliably:

figure;ax1 = axes('xcolor','m','ycolor','m');
ax2 = axes('position',[0 0 1 1],'color','none');
rPosition = rectangle('parent',ax2,'position',get(ax1,'position'),'edgecolor','k');

rectangle shows up in wrong place:

but if i subsequently draw a rectangle at outerposition, all of a sudden the position/black rectangle is in the right place:

rOuter = rectangle('parent',ax2,'position',get(ax1,'outerposition'),'edgecolor','r');

edit: actually drawing any subsequent rectangle in ax2 in a position set as either get(ax1,'outerposition') or 'tightinset' will re-position the first rectangle properly

interestingly, if i get(ax1,'position') before and after the second rectangle is drawn i get the same values:

[0.1300    0.1100    0.7750    0.8150]

ideas? thanks

7.9.1.671 (R2009b) Service Pack 1 (linux 64bit)

Answer 1

[Jan]

I see -and expect- the same behaviour under Matlab 6.5/2009a/2011b under Windows.

Drawing the rectangle in the ax2 object causes an automatic scaling of the X- and Y-limits. Therefore the visible position is shifted. You can avoid this by setting the limits explicitely:

figure;
ax1 = axes('xcolor', 'm', 'ycolor', 'm');
ax2 = axes('position', [0 0 1 1], 'color', 'none', ...
           'XLim', [0, 1], 'YLim', [0, 1]);
rectH = rectangle('parent', ax2, ...
                  'position', get(ax1,'position'), ...
                  'edgecolor','k');

This behaviour explains also, why the subsequent drawings seem to fix the problem - it happens by accident by resetting the limits to the necessary size.

[Eric]

thanks for explaining this behavior. i can see this is try by monitoring x/ylim. but i still don't understand why matlab would do this.

the defaults for xlim and ylim in this case are [0 1] same as you explicitly set.

after the first rectangle is drawn they are indeed scaled as you say:

get(ax2,'xlim') -> [0.1 0.1]

(ylim) is now also the same as new xlim

but these don't make any sense as the position of the rectangle is:

get(rPosition,'position')

ans =

0.1300 0.1100 0.7750 0.8150

what am i missing? or is this indeed a bug as i see it right now

[Jan]

@Eric: I assume a typo: The limits of ax2 are [0.1, 1.0].

This is the intented auto-scaling. Matlab chooses "nice" limits at powers of 10 or multiples of them. Try this:

figure; AxesH = axes; line([0.13, 0.13+0.775], [0.11, 0.11+0.815]); drawnow; get(AxesH, 'XLim')

Again you see that the limits are set to [0.1, 1.0] with auto-scaling and an object with a position of [0.13, 0.11, 0.775, 0.815]. I do neither see an unexpected behaviour nor a bug.

[Eric]

ah. i must not be able to read on weekends. thanks!