How do I vary color along a 2D line?

I am plotting the x,y position of a point over time. I have the data in two vectors, xpos and ypos, and I plot the path of this point using plot(xpos,ypos).

I would like to have this line change color gradually, representing the time axis ( or the index of the x, y vectors).

Is there an easy way to do this?

[Rajiv]

Can be show line plot with different color, if not to use the surface plot as Matt did.

Answer 1

[Matt Fig]

This is one of the classic 'tricks' of MATLAB graphics.

x = 0:.05:2*pi;
y = sin(x);
z = zeros(size(x));
col = x;  % This is the color, vary with x in this case.

surface([x;x],[y;y],[z;z],[col;col],...
        'facecol','no',...
        'edgecol','interp',...
        'linew',2);

EDIT

Changed edgecolor to interp and linewidth to 2. This looks less ragged on my machine.

[Guy]

Respectfully, this works very well for monotonic x or if the intent is to vary color vs. x. But I've found it doesn't really solve the intent of the original question (which is the same thing I'm trying to do) which is to vary the color vs time.

For example, change the above code to have:

x=[1 2 3 4 5 6 5 4 3 2 3 4 5];

y=1:length(x);

As-is, the line will go from blue to red, then back towards blue, then back towards red as y increases. It should go from blue to red with no back-tracking of color if the intent is to plot color vs. time.

Is there a simople way to make it do this? Paulo Silva's 2nd version, below, seems to fit the bill ... but now I have to figure out how to set MyColorOrder to start at blue and end at red (which is probably easier if I knew what I was doing)

On a side note, is there anywhere we can find a treasure trove of all these classic tricks of MATLAB?

[Walter Roberson]

You can start a Question about the classic tricks. Just keep in mind that after enough uses, we tend to stop thinking about them as "tricks" and just let our fingers type them.

MyColorOrder can be any 2D array whose columns are R, G, B, same as a colormap.

[Guy]

Walter,

So I need to suffer just because you guys are so stinking smart?!?!?! Just kidding! I'm sure there are so many tricks that you'd never be able to go through them all to know that one that does what you want even exists. I guess that's what Google and this site are for (which is how I found this 'trick').

I think I've figured it out on my own (for once). Matt's method will plot vs. time if you change:

col = x;

to

col = 1:length(x);

Paulo's method below has a drawback in that it breaks the line into single-color segments. So a) it's not fully continuous, b) it takes a long time to plot if x is long. Otherwise, it's good too ... just not as good as Matt's, in my humble opinion.

[Walter Roberson]

As Nakor would say, All magic is a trick. ;-)

[Rajiv]

Can be show line plot with different color, if not to use the surface plot as Matt did.

[Colby]

I am having one issue when modifying my color bar after using this "trick". I successfully executed a similar code to the one suggested by Matt and added a colorbar to the plot. I have the handle for the color bar and can change the ticks, ticklabels, ect. What I would like to do is have the same scale for my colorbar for multiple plots. When I use "clim" or "caxis" the scale of the color bar is changed successfully, but I get numbers all over the plot. The numbers are associated with the axes labels. I have tried several things like removing ticks and labels and adding them again ect., but I get the same result. This issue only happens after modifying the scale of my colorbar. Any ideas on how to solve this problem?

[Jasmeet Singh]

The above method is giving the following warning for me:

Warning: Error creating or updating Surface Error in value of property ZData Array is wrong shape or size

My x values are real positive numbers but y values include both -Inf and NaN. Do I have to get rid of these non-finite values before plotting or the problem is something else?

[Jason Fevang]

I had this problem, and I had to transpose my vectors before it worked

[Dorian Hargarten]

@Loginatorist, this is an awesome trick, thank you very much!

[Image Analyst]

Adding the plot so we can actually see what it looks like:

x = linspace(0, 2*pi, 1920); % HDTV resolution.
y = sin(x);
z = zeros(size(x));
lineColor = x;  % This is the color, it varies with x in this case.
% Plot the line with width 8 so we can see the colors well.
surface([x;x], [y;y], [z;z], [lineColor;lineColor],...
	'FaceColor', 'no',...
	'EdgeColor', 'interp',...
	'LineWidth', 8);
grid on;

[Roy Goodman]

I tried this for something I'm working on, and am getting a weird artifact:

Each of the 6 edges of this tetrahedron are computed using the line

surface([x1 x1]',[x2 x2]',[x3 x3]',[y y]',...
    'facecolor','none','edgecolor','interp','linewidth',6);

where the arrays x1, x2, x3 parameterize a straight line in 3D space, and y is constant on three of the edges and a monotonically varying sigmoidal function on the other three edges. As you can see from this image, the color index looks very non-monotonic and even noisy on the three edges where the solution varies.

The included graphic was created using the print command, but this is how it appears on the screen as well.

I've tried a few tricks to fix it, neither of which helped

• reducing the number of colors in the colormap
• changing the 'edgecolor' to 'flat'

Answer 2

[KSSV]

x = 0:.05:2*pi;
y = sin(x);
z = y;
patch([x nan],[y nan],[z nan],[z nan], 'edgecolor', 'interp'); 
colorbar;colormap(jet);

[s yuan]

'patch' is helpful for my task, thanks a lot.

Answer 3

[Daniel Refy]

N=1 numel(data(:,1)) for a=1:N:numel(data(:,1))-N plot(data(a:a+N,1),data(a:a+N,2),'.','Color',[(a/numel(data(:,1))),0,0] ) hold on end

this will change color of the line from black to red

[Ariel Szklanny]

This worked great for me, thanks!

Answer 4

[Paulo Silva]

Something similar to this:

plot(xpos(1:10),ypos(1:10)) %first points in blue
plot(xpos(11:20),ypos(11:20),'g') %green ones
plot(xpos(21:end),ypos(21:end),'r') %final points in red

another way, the hold all function makes the plots with different color (until the list of available colors ends and after it start from the first one again)

clf
hold all
plot(xpos(1:10),ypos(1:10)) 
plot(xpos(11:20),ypos(11:20)) 
plot(xpos(21:31),ypos(21:31)) 
... %more plots until the end of the indexes

You can insert the code inside a for loop

clf 
hold all
N=7; %every N points change color
for a=1:N:numel(xpos)-N
plot(xpos(a:a+N),ypos(a:a+N)) 
end

[Kathryn McCormick]

Thanks for the reply. I want to vary the color continuously, not in chunks.

[Paulo Silva]

You can change the order of the colors and give the impression of it being continously.

axes

MyColorOrder=get(gca,'ColorOrder'); %RGB combinations per row

%make your own color order, you can even add more row (more possible colors)

set(gca,'ColorOrder',MyColorOrder); %RGB combinations per row

hold all

N=7; %every N points change color

for a=1:N:numel(xpos)-N

plot(xpos(a:a+N),ypos(a:a+N))

end