How would you make a contour plot of a 3 column matrix?

Hello,

I am currently trying to make a contour plot of distance-depth with pCO2 as the z value (in the excel file there are multiple columns but i only need those three). This takes the form of three columns of equal size, however I looked in the forums and it is apparently not possible. Data from the third column needs to be associated to the others in some way that allows the contour plot. My question is: if not possible, how then would you represent a profile such as this, with distance on x, depth on y and z as the value studied ?? I have thought about a scatter but I can't figure out the parameters to trace for example lines of equal values to make it look better than just scattered points... Any ideas ?? Thank you !!

[Wick]

Edit: I didn't see the Excel spreadsheet on first pass. The answer section has my code to solve this for you.

Answer 1

[John BG]

Hi Louis van Herwijnen

this is John BG <mailto:[e-mail] [e-mail]>

1.-

acquiring data from the provided Excel file

clear all;clc;close all
A=xlsread('AR07W_2011processed.xls')

L=A(:,1)                         % reading distances

taking only 2 decimals

N=2
L=1/10^N*floor(L*10^N)

.

checking whether grid is uniform

.

[D,ni,na]=unique(L);             

ni(1)=1   % correction for 1st row because spreadsheet 1st row contains var names only, not numerical data

nD=[diff(ni); numel(L)-ni(end)+1]  % amount of measurements at different depths, on same distance

.

The coordinates to use are D: Distance W: Depth

.

d=A(:,1);
w=A(:,2);

% max min values of coordinates:
min(d)
% =
%      0

max(d)
%  =
%      6.887000000000001e+02

min(w)
%  =
%    1.400000000000000

max(w)
% =
%      3.675300000000000e+03

.

ok, now we see it's a non-uniform grid

2.-

 acquiring measurements

T         =  A(:,3);      % Temperature Celcsius
S         =  A(:,4);      % Salinity [psu]
TA        =  A(:,4);      % TA umol/kgSW
TCO2      =  A(:,5);      % TCO2 umol/kgSW
TpCO2     =  A(:,6);      % pCO2 uatm
pH        =  A(:,7);      % pH
O2        =  A(:,8);      % O2 [umol/kgSW

3.-

Example plot without interpolation, on same distance

k=3
hf(1)=figure(1);plot(w([ni(k):1:ni(k+1)-1])',T([ni(k):1:ni(k+1)-1])')
xlabel('W:depth');ylabel('T(ºC)')
title(['Temperature measurements at distance d = ' num2str(d(ni(k)))]);
grid on
% 000-1

.

non-uniform grid of 2D reference points

.

hf(2)=figure(2);plot(d,w,'ro');grid on;grid minor
xlabel('D:distance');ylabel('W:depth')
% 000-2

.

Temperature interpolation

.

F_Temperature=scatteredInterpolant(d,w,T)
% F=scatteredInterpolant(A(:,1),A(:,2),A(:,3))

Q=4  % interpolation factor 
d_uniform_range=linspace(min(d),max(d),Q*numel(nD)-1)
w_uniform_range=linspace(min(w),max(w),Q*numel(nD)-1)
[D,W]=meshgrid(d_uniform_range,w_uniform_range)
T2=F_Temperature(D,W)
hf(3)=figure(3);surf(D,W,T2)
campos([4401.80925645085   23683.44745915113   25.18900384688])
xlabel('D:distance');ylabel('W:depth')
title(['Temperature - interpolation factor Q = ' num2str(Q)])
% 001

.

4.- Temperature contours

.

hf(4)=figure(4);hT_surfc=surfc(D,W,T2)
campos([5578.878486985600   7013.723961265031   21.490607228584])
xlabel('D:distance');ylabel('W:depth')
title('Temp contour projections')
% 002

.

The projected contours are available in here:

 hT_surfc(2)
 ans = 
   Contour with properties:

     LineColor: 'flat'
     LineStyle: '-'
     LineWidth: 0.500000000000000
          Fill: 'off'
     LevelList: [1×9 double]
         XData: [71×71 double]
         YData: [71×71 double]
         ZData: [71×71 double]

.

You can carry on working on the contour lines by acquiring the 2D curves in the following way:

x_T_contours=hT_surfc(2).XData
y_T_contours=hT_surfc(2).YData
z_T_contours=hT_surfc(2).ZData

hf(5)=figure(5);contourf(T2,10)
xlabel('D:distance');ylabel('W:depth')
title('Temperature contours with contourf')
% 003

.

Once a surface is available it may be particularly useful to 1: zoom in and out and 2: check data with the cursor, that I prefer call it marker:

.

5.-

Salinity [psu] Surface

.

F_Salinity=scatteredInterpolant(d,w,S)
S2=F_Salinity(D,W)
hf(6)=figure(6);surf(D,W,S2)
campos([4401.80925645085   23683.44745915113   25.18900384688])
xlabel('D:distance');ylabel('W:depth')
title(['Salinity - interpolation factor Q = ' num2str(Q)])

hf(7)=figure(7);hS_surfc=surfc(D,W,S2)
campos([5578.878486985600   7013.723961265031   21.490607228584])
xlabel('D:distance');ylabel('W:depth')
title('Salinity contour projections')
% 004

x_S_contours=hS_surfc(2).XData;
y_S_contours=hS_surfc(2).YData;
z_S_contours=hS_surfc(2).ZData;

hf(8)=figure(8);contourf(T2,10)   
xlabel('D:distance');ylabel('W:depth')
title('Temperature contours with contourf')

6.-

TA [umol/kgSW] surface

F_TA=scatteredInterpolant(d,w,TA)
TA2=F_TA(D,W)
hf(9)=figure(9);surf(D,W,TA2)
campos([4401.80925645085   23683.44745915113   25.18900384688])
xlabel('D:distance');ylabel('W:depth')
title(['TA - interpolation factor Q = ' num2str(Q)])

hf(10)=figure(10);hTA_surfc=surfc(D,W,S2)
campos([5578.878486985600   7013.723961265031   21.490607228584])
xlabel('D:distance');ylabel('W:depth')
title('TA contour projections')
% 005

x_TA_contours=hTA_surfc(2).XData
y_TA_contours=hTA_surfc(2).YData
z_TA_contours=hTA_surfc(2).ZData

hf(11)=figure(11);contourf(TA2,10)   
xlabel('D:distance');ylabel('W:depth')
title('TA contours with contourf')

7.- TCO2 [umol/kgSW] surface

F_TCO2=scatteredInterpolant(d,w,TCO2)
TCO22=F_TCO2(D,W)
hf(12)=figure(12);surf(D,W,TCO22)
campos([4401.80925645085   23683.44745915113   25.18900384688])
xlabel('D:distance');ylabel('W:depth')
title(['TCO2 - interpolation factor Q = ' num2str(Q)])

hf(13)=figure(13);hTCO2_surfc=surfc(D,W,TCO22)
campos(   1.0e+04 *[  -0.486868459634731   1.534198637901339   0.281087905547732])
xlabel('D:distance');ylabel('W:depth')
title('TCO2 contour projections')
% 006

x_TCO2_contours=hTCO2_surfc(2).XData
y_TCO2_contours=hTCO2_surfc(2).YData
z_TCO2_contours=hTCO2_surfc(2).ZData

hf(14)=figure(14);contourf(TCO22,10)   
xlabel('D:distance');ylabel('W:depth')
title('TCO2 contours with contourf')

8.- pCO2 [uatm] surface

F_TpCO2=scatteredInterpolant(d,w,TpCO2)
TpCO22=F_TpCO2(D,W)
hf(15)=figure(15);surf(D,W,TpCO22)
campos([4401.80925645085   23683.44745915113   25.18900384688])
xlabel('D:distance');ylabel('W:depth')
title(['TpCO2 - interpolation factor Q = ' num2str(Q)])

hf(16)=figure(16);hTpCO2_surfc=surfc(D,W,TpCO22)
campos(   1.0e+04 *[  -0.486868459634731   1.534198637901339   0.281087905547732])
xlabel('D:distance');ylabel('W:depth')
title('TpCO2 contour projections')
% 006

x_pCO2_contours=hTpCO2_surfc(2).XData
y_pCO2_contours=hTpCO2_surfc(2).YData
z_pCO2_contours=hTpCO2_surfc(2).ZData

hf(17)=figure(17);contourf(TpCO22,10)   
xlabel('D:distance');ylabel('W:depth')
title('TpCO2 contours with contourf')

9.- Acidity [pH] surface

F_pH=scatteredInterpolant(d,w,pH)
pH2=F_pH(D,W)
hf(18)=figure(15);surf(D,W,pH2)
campos([4401.80925645085   23683.44745915113   25.18900384688])
xlabel('D:distance');ylabel('W:depth')
title(['pH - interpolation factor Q = ' num2str(Q)])

hf(19)=figure(16);hpH_surfc=surfc(D,W,pH2)
campos(   1.0e+04 *[  -0.486868459634731   1.534198637901339   0.281087905547732])
xlabel('D:distance');ylabel('W:depth')
title('pH contour projections')
% 006

x_pH2_contours=hpH_surfc(2).XData
y_pH2_contours=hpH_surfc(2).YData
z_pH2_contours=hpH_surfc(2).ZData

hf(20)=figure(17);contourf(pH2,10)   
xlabel('D:distance');ylabel('W:depth')
title('pH contours with contourf')

10.- Oxygen O2: [umol/kgSW] surface

F_O2=scatteredInterpolant(d,w,O2)
O22=F_O2(D,W)
hf(21)=figure(15);surf(D,W,O22)
campos([4401.80925645085   23683.44745915113   25.18900384688])
xlabel('D:distance');ylabel('W:depth')
title(['O2 - interpolation factor Q = ' num2str(Q)])

hf(22)=figure(16);hO2_surfc=surfc(D,W,O22)
campos(    1.0e+04 *[-0.461106553630150   1.377458945573147   0.001065817992402])
xlabel('D:distance');ylabel('W:depth')
title('O2 contour projections')
% 006

x_O22_contours=hO2_surfc(2).XData
y_O22_contours=hO2_surfc(2).YData
z_O22_contours=hO2_surfc(2).ZData

hf(23)=figure(17);contourf(O22,10)   
xlabel('D:distance');ylabel('W:depth')
title('O2 contours with contourf')

.

saving results

.

save('Excel_TSal_et_al_variables.mat')    % load with : load(''Excel_TSal_et_al_variables.mat'')
savefig(hf,'AllFigures.fig')                       % load with : openfig('AllFigures.fig')

Louis

if you find this answer useful would you please be so kind to consider marking my answer as Accepted Answer?

To any other reader, if you find this answer useful please consider clicking on the thumbs-up vote link

thanks in advance for time and attention

John BG

<mailto:[e-mail] [e-mail]>

[Louis van Herwijnen]

Thank you John this was incredibly helpful !! I hope it didn't take you too long to write all this, but this is perfect !!

[John BG]

Hi Louis, on the contrary, some questions jam and additional time is required but I solved similar questions the solving was on schedule.

Happy to help.

Feel free to contact me regarding MATLAB questions with a link to any new question you decide to post so I can have a look.

[Katherina Fiege]

Hi John,

which toolbox does contain the command "acquire measurements"? this is what currently holds my progress with the code you provided.

I'd be very happy if you would answer!

Best,

Kat

Answer 2

[Wick]

This plots the original data, the mesh that interpolates that data, and the contours it creates. If you want it to extrapolate outside of the values of data reported, remove the 'non' from the 'scatteredInterpolant' command.

    clearvars
    A = xlsread('AR07W_2011processed.xls');
    distance = A(:,1);
    depth = A(:,2);
    pCO2 = A(:,7);

    clf
    plot3(distance, depth, pCO2,'o');
    hold on

    x = linspace(min(distance), max(distance), 1000);
    y = linspace(min(depth),max(depth), numel(x))';
    [XX, YY] = meshgrid(x,y);
    F = scatteredInterpolant(distance, depth, pCO2,'linear','none');
    ZZ = F(XX,YY);

    mesh(XX,YY,ZZ);
    contour(XX,YY,ZZ,50)

    hold off

[Louis van Herwijnen]

Hello Chad,

Thank you for your time !! Your answer is almost what I am looking for, only it gives me the following figure:

This is almost perfect however I would like to keep only the 'flat' part on the bottom, I'll use the colorbar to indicate the values of z. how would I remove the 3rd axis (so the one for the values of pCO2) to have basically a 2d plot ?? otherwise this is almost exactly what I need thank you very much !!

[Louis van Herwijnen]

For example I have just tried replacing: clf plot3(distance, depth, pCO2,'o'); hold on by: clf plot(distance,depth,'o') hold on

so that the following calculations plot on a 2d plot and I get the following:

which is the sort of depth profile I need but it is not completely proper you can still see the other data beneath...

[Wick]

simply remove the line with the 'plot' command if you don't want to see the data.

There were three separate plotting commands I used. All can be used alone or together. Those commands are 'plot3', 'contour', and 'mesh.'

You might also try 'pcolor' and 'surf.' I suggest reading about plotting options in the tutorials and help section.

[Louis van Herwijnen]

Thank you this helped me a lot !!! thank you again !!