colored Line plot according to a third variable

Hello,

I already asked this question before but it is really important to have an answer since the last answer i got wasn't helpful.

i will post the whole code:

"hold on

load(Filename.mat')

low=20;

high=30;

for i=1:235

f=find(vr(:,1)==i); vr indexes are from 1 to 235 but vr is 11000 rows and 0 columns

indexfmax=f(1,1);

indexfmin=f(end,end);

lamda=(vr(f,3)./vr(f,2));% range between 20 and 30

index1=find(lamda>=low & lamda<=high);

maxindex=max(index1);

minindex=min(index1);

x(1,i)=sqrt((vr(f(1,1),8)-vr(f(1,1),6))^2 + (vr(f(1,1),9)-vr(f(1,1),7))^2);%x here is the length for each path

reference(1,i)=sqrt((vr(f(1,1),6))^2 + (vr(f(1,1),7)^2));

if isempty(index1)

averageV(1,i)=NaN;

else

averageV(1,i)=mean(vr(minindex:maxindex,3));

end

end

path1=find(x>=59 & x<=61); path2=find(x>=79 & x<=81);

% For low=20

if low==20

for j=1:47 %path1

if low==20

if rem(j,2)==0

y(1,j:47)=20;

else

y(1,j:47)=21;

end

p1(:,j)=[reference(1,path1(1,j)) y(1,j)];

p2(:,j)=[reference(1,path1(1,j))+x(1,path1(1,j)) y(1,j)];

end

end

averageV=round(averageV);

normalized=averageV/max(averageV);

for j=1:47

if (~isnan(normalized(1,path1(1,j))))

% plot([ p1(1,j) p2(1,j)], [p1(2,j) p2(2,j)])

plot3([ p1(1,j) p2(1,j)], [p1(2,j) p2(2,j)],[normalized(1,path1(1,j)),normalized(1,path1(1,j))],'Linewidth',1);

else

continue;

end

end

colorbar

xlim([0 2000]);

ylim([0 100])"

how can i specify the color of the line plotted by joining the 2 points p1 and p2 according to its corresponding velocity from matrix 'normalized' OR 'averageV'

the averageV could contain velocity as NaN or between 400 and 1200 and after knowing the min and max, the color should be distributed between them (yellow to blue for example) and each velocity corresponds to a color. is that possible ? because it's been 3 months and it didnt work so maybe it's not possible to do that in matlab?

Answer 1

[darova]

clc,clear

    % generate some data
x = linspace(0,10,10);
y = x.^2;
x = [ x nan ];                % i added nan for 'patch' function
y = [ y nan ];
n = length(x);
vel = 10*rand(1,n);           % generate some velocities

Then i was HERE to choose correct colormap. parula looks ok

cm = parula(n);

You can also choose another colormap e.g. jet nad take about 2/3 colors

% cm = jet( round(3/2*n) );   % generate more colors
% cm = cm(1:n,:);             % take only 2/3

You can interpolate your velocities to indificate correct colors

ind = interp1([min(vel) max(vel)], [1 n], vel);        % get indices of colors for each velocity
ind = round(ind);                                      % indices have to be integer
cm = cm(ind,:);                                        % choose colors from colormap

You can plot data using plot(). Just draw each segment seprately and assign appropriate color

hold on
for i = 1:length(x)-1
    j = i:i+1;
    plot(x(j),y(j),'o-r','color',cm(i,:))
end
hold off

Or you can use patch(). Pay attention that patch has interpolation property

patch(x,y,'', 'EdgeColor','interp', ...
            'FaceVertexCdata',cm, ...
            'Linewidth', 2);
hold on
plot(x,y,'or')
hold off

[Michel tawil]

I added these, it didn't work, it gave this error first:

Subscript indices must either be real positive integers or logicals.

Error in trial2 (line 56)

cm=cm(ind,:);

"n=length(p1);

cm=parula(n);

ind=interp1([min(averageV) max(averageV)],[1 n],averageV);

ind=round(ind);

cm=cm(ind,:);

for j=1:47

if (~isnan(normalized(1,path1(1,j))))

plot([ p1(1,j) p2(1,j)], [p1(2,j) p2(2,j)],'o-r','color',cm(j,:));

else

continue;

end

end"

[darova]

Why?

Answer 2

[Michel tawil]

the ind generated is 235 column and 1 row ( same as averageV) but withing the averageV, some of the velocities are NaN which means that ind not only contains values of the averageV but also NaNs

[darova]

Is it possible to solve this?

[Michel tawil]

yes, i tried to remove the nan and i have obtained ind matrix of 27 columns and 1 row. now i guess i need to work with the index j for cm because it goes from 1 to 47 and ind has 27

[darova]

What should i do?