make grid

hello,, i have a problem like this.. i want to make grid (i give its color red) like this picture: http://www.flickr.com/photos/rye_ni/7063578237/

the grid divide the width and height of image.. so, it have 4 areas.. when i press a button, automatically the grid will be show.. how i can make like that.. thank you.. ^^

Answer 1

[Walter Roberson]

xL = get(gca, 'XLim');
yL = get(gca, 'YLim');
xcen = mean(xL);
ycen = mean(yL);
gridlines = line([xcen xcen nan xL], [xL nan ycen ycen], 'Color', [1 0 0]);

[Rahma Yeni]

Thank you Walter.. ^^