plot one curve with two colors

Dears, am plotting the response of an sensor with one curve in real time, and i want to plot this curve with two colors, depending on the values of the returned data, when data<500 the curve is plotted in "red" when data>=500 the curve is plotted in "green" so i need to plot one curve with two colors. best regards

Answer 1

[Star Strider]

There may be more efficient methods, but this works:

t = linspace(0, 3*pi, 500);
y = 200*sin(t) + 400;

ygidx = (y >= 500);             % Define ‘Green’ Regions
tg = t;
yg = y;
yg(ygidx == 0) = NaN;
tg(ygidx == 0) = NaN;

figure(1)
plot(t, y, '-r')
hold on
plot(tg, yg, '-g')
hold off

You may have to experiment with it to get the result you want.

[gregor alexander]

thnx alot

[Star Strider]

My pleasure!

Answer 2

[Kelly Kearney]

If you plot with a patch rather than a line, you can get the color change. Depending on how much the y-values oscillate across the boundaries, you may need to upsample your data first to get a clean color transition (this particular example needed a lot of upsampling, since the values switch back and forth so much... a smoother curve won't need that):

x = 1:100;
y = rand(1,100)*1000;

xi = linspace(x(1), x(end), 5000);
yi = interp1(x,y,xi);
ci = yi < 500;

h = patch([xi NaN], [yi NaN], [ci NaN]);
set(h, 'edgecolor', 'interp');
colormap([0 1 0; 1 0 0]);

[gregor alexander]

thnx a lot