import data and plat a 3D

I do have a excel file with 3 columns (x y z). I wanna import them to Matlab, and plot a nice surface Plot.i might have to interpolate?

[Rik]

If it is a full grid of x and y, there will be no need for interpollation. Can you share your actual data, or a functional equivalent?

[Verena Salan]

here are my data

Answer 1

[Rik]

No interpollation required, just a conversion to a 2D matrix. You can adapt the syntax of accumarray if you do have any missing values (by default it will fill with 0).

num=xlsread('test1.xlsx');
x=num(:,1);
y=num(:,2);
P=num(:,3);

%find the unique x and y values and use them as indices to fill the Z
[X,~,x_]=unique(x);
[Y,~,y_]=unique(y);
Z=accumarray([x_,y_],P);
[X,Y]=ndgrid(X,Y);

surf(X,Y,Z)

[Verena Salan]

Hi

thank you very much.

I got 2 hills. Do you know how i can get the volume from the right hill?

[ME]

Nice solution. You could also use the reshape function to get your z-data into the correct format.

I had assumed the data wouldn't be uniform over x and y - I suppose I should ask more questions in future!

[Verena Salan]

@ME : how would it look like with the reshape function?

[Rik]

The reshape method has the downside that you need to be sure about the orientation of your data. It will also fundamentally break if you don't have a complete grid.

Also note that surf will handle non-uniform spacing of values, it just needs a full grid (which is allowed to contain NaN values).

As to the question of how to get the volume: figure out a way to set the other hill to 0 and then use a 2D integration to find the volume.

[Verena Salan]

Because of the volume, can't figure out how to do that.

[Rik]

What have you tried?

[Verena Salan]

Does anyone has any ideas how i could get the volume? don't know how.

[Rik]

What have you tried so far?

[Verena Salan]

don't know how

[Rik]

On a conceptual level, what would you do? If you needed to do it on paper, what would your approach be?

Answer 2

[ME]

I think you are correct about the need to interpolate. You could try having a read of the link below - that should give you some good pointers.

https://uk.mathworks.com/help/matlab/math/interpolating-scattered-data.html