plot 3D curve with color-coded direction

Question

Liang Zhan 2012-7-30

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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

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Answer 1

Teja Muppirala 2012-7-31

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在 MATLAB Online 中打开

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

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Walter Roberson 2012-7-31

Teja, continuous curves plotted with plot() or plot3() cannot change color as they progress.

Teja Muppirala 2012-7-31

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.

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Answer 2

Walter Roberson 2012-7-31

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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 ?