# plot 3D curve with color-coded direction

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Liang Zhan on 30 Jul 2012
hi, friends,
I have a 3xN matrix, which represents N points in one curve. I know plot3 can plot this curve easily, but I want to use color to represent the curve orientation. For example, if the curve is in x direction, the color is "red", if the curve is in y direction, the color is in "green", if the curve is in z direction, the color is in "blue“.
So the color will vary with the curve going from the beginning to the end.
I saw some example from other software, want to know whether it can be done in matlab.
Appreciate!
LZ

Teja Muppirala on 31 Jul 2012
Yes, you can do this in MATLAB. But it is easier to use a "surface" (in this case, I am calling MESH) to plot it instead of a line.
%Make a random 3d curve
P = interpft(rand(10,3),500);
P(end+1,:) = P(1,:);
% Make colors from the velocity
dP = diff(P([1:end 1],:));
C = abs(dP)/max(abs(dP(:)));
C = permute(cat(3,C,C),[1 3 2]);
% Use mesh to draw it
h = mesh([P(:,1) P(:,1)],[P(:,2) P(:,2)],[P(:,3) P(:,3)],C);
set(h,'lineWidth',3);
axis vis3d
##### 2 CommentsShowHide 1 older comment
Teja Muppirala on 31 Jul 2012
Hi Walter, I meant that if he were to try to do it using lines, he would have to make many different line objects, one for each segment in a different color. That is not impossible, but it is kind of a hassle. That is why I agree with your suggestion below that surfaces (patches) are a more general and easier way to accomplish the same thing.

### More Answers (2)

Walter Roberson on 31 Jul 2012
line() and lineseries objects such as are generated by plot() and plot3(), are each restricted to one color along the length. For this reason, some people prefer to instead use very narrow patch() objects; the edgecolor of patch objects can be controlled.
Question: if A, B, C are three consecutive points, with different "trends" between A-B and B-C, then should the line between A-B be all one color, and the line between B-C be all a different color, or do you want the color changes to shade between the points ?

Liang Zhan on 31 Jul 2012
Thanks Teja Muppirala, your code works very well in my case, appreciate! Also, thanks Walter Roberson for your input