contour plot based on xyz data

I have xyz data as attached. X is longitude, y is altitude and z is electron density. For each value of longitude from 75 to 95, I have altitude values of 100 to 2000 with corresponding electron density values for each altitude. I want a colored contour plot with these data. Please help.

Answer 1

[Star Strider]

Your data are gridded. You only need to reshape them into your ‘X’, ‘Y’, and ‘Z’ matrices:

D = load('data_new.txt');
[Du,D1] = unique(D(:,1));
Dd = diff(D1);
Dr = reshape(D, Dd(1), [], size(D,2));
X = Dr(:,:,1);
Y = Dr(:,:,2);
Z = Dr(:,:,3);

figure
contourf(X, Y, Z)

See the documentation on contourf (link) for details on how to customise it.

[wadah mahmoud]

Dear Star Strider

Thank you for the providing code, I used it and it is very helpful for me but i need your assiatnce in " how to calculatethe maximum point and showing it on the plot" , if you need I will provide you a text file of values.

Thank you for assistance.

Wadah

[Adam Danz]

"how to calculatethe maximum point and showing it on the plot"

[maxY, maxX] = find(Z == max(Z(:))); 
hold on
plot(X(maxX), Y(maxY), 'rx')

If you'd like to select the entire contour that surrounds the max value, you can use getContourLineCoordinates() from the file exchange like so,

cm = contourf(X,Y,Z); 
contourTable = getContourLineCoordinates(cm);
maxLevel = max(contourTable.Level); 
xMaxLevel = contourTable.X(contourTable.Level == maxLevel);
yMaxLevel = contourTable.Y(contourTable.Level == maxLevel);
hold on 
plot(xMaxLevel, yMaxLevel, 'r.', 'MarkerSize', 10)

Answer 2

[jonas]

You just need to interpolate gridded data.

xyz=dlmread('data_new.txt');
x=xyz(:,1);
y=xyz(:,2);
z=xyz(:,3);
[X,Y]=meshgrid(min(x):max(x),min(y):max(y));
Z=griddata(x,y,z,X,Y);
contour(x,y,Z)

[youssef aider]

works but, still gives some fluctuations

[Daniyal Altaf Baloch]

Hi Jonas. Your answer perfectly works except for the typo in the last line.

Instead of

contour(x,y,Z)

it should be

contour(X,Y,Z) i.e capital X and Y will work .