How do I assign certain colours to different sections of a 3plot?

I have a 4 column matrix. The first column is assigned a number, 99,104 or 115 and the last three columns represents a position x,y,z in a 3D space. Each number in the first column represents a colour, 99-green, 104-red and 115-blue. How could I plot this 3D data with respect to the assigned colours?

Answer 1

[Walter Roberson]

cmap = zeros(115,3);
cmap(99,:) = [0 1 0];   %99 is green
cmap(104,:) = [1 0 0];   %104 is red
cmap(115,:) = [0 0 1];   %115 is blue
pointsize = 40;
scatter3(YourMatrix(:,2), YourMatrix(:,3), YourMatrix(:,4), pointsize, YourMatrix(:,1));
colormap(cmap);
caxis([1,115])

This makes use of the fact that your particular values are small positive integers, and uses them as indices into a colormap that has been created to have the desired colors at those values. Then it says to map "1" to the bottom color, "115" to the top color -- essentially mapping 1 to 1 for the 115 entry color map.

[shellmcg]

Thank you Walter Roberson,

Could you use this code with plot3? I have tried to use plot3 with this code i.e.

plot3(YourMatrix(:,2), YourMatrix(:,3), YourMatrix(:,4), LineSpec, YourMatrix(:,1)); 
colormap(cmap);

and I keep getting errors.

Thanks again for the help

[Walter Roberson]

No. plot3() is for lines. Each line must have the same color. The closest you could get would be to plot3() the line into place with a constant color, and also scatter3() colored markers.

[shellmcg]

Would there be a way to separate the data in sections but keep each section in the original series and then use plot3 on each section i.e if I had a matrix

99 x y z;
99 x y z;
99 x y z;
104 x y z;
104 x y z;
99 x y z;
etc

so some how get matlab to plot3 the first section of 99s then plot3 again the second section of 104s and continue on until the end of the matrix?

[Walter Roberson]

Yes, that could be done. However, what color should the lines be on the segment joining the 99 to 104 and so on?

[shellmcg]

The colour of the joining segment would be the colour of the previous segment. so the segment between 99 to 104 would be green. Thanks again for your help

[shellmcg]

HI Walter,

I have written the following script using the your color mapping to plot the data in sections of color but am getting errors. any suggestions?

    for i=1:length(YourMatrix);
        start=1;

    if YourMatrix(i,1)~= YourMatrix(i+1,1)
           plot3(YourMatrix(:,2),YourMatrix(:,3),YourMatrix(:,4),'color',YourMatrix(:,1));
         colormap(cmap);
          start=i+1;
        end
    end

[Walter Roberson]

codes = [inf; YourMatrix(:,1); -inf]);
breakpoints = find(diff(codes));
breakpoints(end) = breakpoints(end)-1;  %reaches one past end
for K = 1 : length(breakpoints)-1
  startpos = breakpoints(K);
  endpos = breakpoints(K+1);
  plot3(YourMatrix(startpos:endpos, 2), YourMatrix(startpos:endpos, 3), YourMatrix(startpos:endpos, 4), 'color', YourMatrix(startpos,1) );
  hold on
end
hold off
colormap(cmap);