Advanced MATLAB: Surface plot of nonuniform data23

Posted by Doug Hull,

Two minute video shows how to fit a surface to nonuniform data.
Real data is not always on a nice X,Y grid, but the MATLAB commands
SURF and MESH expect them to be. GRIDDATA and MESHGRID help to fix this.

Video Content

Find the files here.

PodCast here

Other videos have been gathered here:
http://blogs.mathworks.com/pick/category/video/

Dear Sir:

I am very grad to find the program of “advanced-matlab-surface-plot-of-nonuniform-data”, but I could not run it
because of no-coincide of matrix dimension.
Would you please inform me of a mistake I coded (copied).

Best Regards,
————————

%3D graph for nonuniform_data
x=rand(100,1)*16-8;
y=rand(100,1)*16-8;
r=sqrt(x.^2+y.^2)+eps;
z=sin(r)./r;
%
xlin=linspace(min(x),max(x),33);
ylin=linspace(min(y),max(y),33);
[X,Y]=meshgrid(xlin,ylin);
Z=griddata(x,y,z,X,Y,’cubic’);
%
mesh(X,Y,Z); % interpolated
axis tight; hold on
plot3(x,y,z,’.’,’MarkerSize’,15)
%%surf(X,Y,Z)

paul replied on : 2 of 23

I copied the code from you message and it worked perfectly on my side! – sorry!

Doug replied on : 3 of 23

The code you pasted here worked exactly right for me too. I am not sure what to do for you.

Sorry,
Doug

Els replied on : 5 of 23

Dear Doug,

This info about making a surface plot was very usefull for me. In stead of the formule that you used to produce some points, I used 4 XYZ-coordinates that result in an surface in 3D. Is there an easy way to calculate the surface area of this created object?

Best regards,
Els

Doug replied on : 6 of 23

Els,

There is no built in function to do this, but knowing the X,Y,Z of each point in the mesh, you should be able to calculate the area of each four point patch. From there, summing should be easy to know the whole area.

Doug

Jim replied on : 7 of 23

I have three column data (time,height,collection) supposedly x,y,z data. I want to plot it and get the equation. How can I do that with Matlab.
eg data:
x – y – z
1 – 1 – 130
2 – 1 – 130
3 – 1 – 130
4 – 1 – 130
7 – 2 – 130
10 – 2 – 130
16 – 2 – 130
25 – 2 – 130
40 – 2 – 130
63 – 3 – 130
100 – 3 – 130
160 – 3 – 130
250 – 3 – 130
300 – 3 – 130
400 – 3 – 130
500 – 3 – 130
1 – 3 – 260
2 – 3 – 260
3 – 3 – 260
4 – 3 – 260
7 – 3 – 260
10 – 3 – 260
16 – 4 – 260
25 – 4 – 260
40 – 4 – 260
63 – 6 – 260
100 – 8 – 260
160 – 10 – 260
250 – 11 – 260
300 – 11 – 260
400 – 11 – 260
500 – 11 – 260
1 – 4 – 390
2 – 5 – 390
3 – 5 – 390
4 – 5 – 390
7 – 6 – 390
10 – 7 – 390
16 – 8 – 390
25 – 10 – 390
40 – 12 – 390
63 – 14 – 390
100 – 15 – 390
160 – 19 – 390
250 – 22 – 390
300 – 26 – 390
400 – 30 – 390
500 – 30 – 390
1 – 4 – 650
2 – 5 – 650
3 – 5 – 650
4 – 5 – 650
7 – 5 – 650
10 – 7 – 650
16 – 8 – 650
25 – 9 – 650
40 – 12 – 650
63 – 14 – 650
100 – 18 – 650
160 – 22 – 650
250 – 27 – 650
300 – 27 – 650
400 – 36 – 650
500 – 40 – 650
1 – 2 – 910
2 – 2 – 910
3 – 2 – 910
4 – 3 – 910
7 – 5 – 910
10 – 5 – 910
16 – 7 – 910
25 – 9 – 910
40 – 15 – 910
63 – 20 – 910
100 – 24 – 910
160 – 32 – 910
250 – 38 – 910
300 – 41 – 910
400 – 46 – 910
500 – 49 – 910

venkat replied on : 8 of 23

I have multiple [x,y,z] matrices of my data with which i want to plot the surface using a 7th order polynomial, how can I do that??

Doug replied on : 9 of 23

Venkat,

I am not sure that I understand the question. If you have x,y,z triples, you just plot them. Are you trying to fit a polynomial to them? That would imply a two dimensional dataset. Are you trying to fit some kind of a surface to the data?

You might be best off looking here:

http://blogs.mathworks.com/pick/how-to-get-help/

It shows how to ask for help at the bottom.

Doug

Daniel replied on : 10 of 23

Hi Doug

Thanks for these videos, they have really helped me alot. I am currently looking to create a surface plot (non uniform data) but I would like to represent it in the z-axis. To explain myself better:

If you think of various layers of semi circles made up of dots, and as you move ‘up’, the number of dots are increasing, so it ends up looking like a funnel. Now the code you presented here creates a surface for each circle (ie. for each layer), but now I want to create a surface joining the layers. I hope I have explained myself adequately. Thanks again and I would really appreciate your input.

Kind Regards

Teja replied on : 12 of 23

Dear Doug
Is there anyway to plot a surface from nonuniform data without meshgrid and griddata? Basically i have topographic information, where the altitude(z) at each x and y is known.
I do not want any interpolation in between. x and y do not form a rectangular grid but are closely spaced.
Thanks

faiz replied on : 14 of 23

i like to use this program..but can someone explai to me, what the number meant ,100,1,16,8 and 33 for below..

x=rand(100,1)*16-8;
y=rand(100,1)*16-8;
xlin=linspace(min(x),max(x),33);

i try to run randomly, but appear error with “cubic” like
The input character is not valid in MATLAB statements or expressions.

Thanks

Doug replied on : 15 of 23

@Faiz

X is a vector of random numbers 100×1. It is then multiplied by 16 and 8 is subtracted from it.

xlin is a vector of lineraly spaced numbers (33 in total) that range from the minimum to the maximum of x.

hadi replied on : 16 of 23

hello
i have 3 sets o data x,y,z and they are nonuniform
how can i make a contour plot of z values?

hadi replied on : 17 of 23

they are bathymetric data which x and y are coordinations and z is the depth at that point
i need contour lines of z value

Mike replied on : 18 of 23

Hi;
I have written the following script based on your lesson. The surface which i end up in seems not be correctly reflect the data point i have. Would you please have a look and tell me what could be wrong here?

X1=[7 8 10 12 8 10 12 12 12 12 12];
Y1=[15.8 16.8 17.8 18.8 17.8 17.8 17.8 15.8 16.8 17.8 18.8];
Z1=[12.6 16.2 36 57.9 47.4 36 30.1 16.4 25.7 30.1 57.9];

CLF();
Xlin=linspace(min(X1),max(X1),30);
Ylin=linspace(min(Y1),max(Y1),30);
[X,Y]=meshgrid(Xlin,Ylin);
Z=griddata(X1,Y1,Z1,X,Y,’Cubic’);
mesh(X,Y,Z);
%axis tight, hold off
%plot3(X1,Y1,Z1,’.’,’Markersize’,15)
%surf(X,Y,Z);

Andrea replied on : 19 of 23

Thanks for the fantastic demonstration. I tried to figure out how to generate surface plots for non-uniform data a couple of times before but never found somebody who was able to explain it to me. I got it know and my surface plot looks fantastic. At those moments I love the internet and the helpful guys like you who give their time to help me understand…
Thank you so much.

Prabhat Man Sainju replied on : 20 of 23

Hi,

I have a set of x,y,z data. The data is mainly SNR,RSRP and Throughput in x,y,z dimensions respectively. While i perform the steps you’ve mentioned, i get the following error:

??? Error using ==> DelaunayTri
The input points must contain finite values; Inf and NaN are not permitted.

Error in ==> griddata>cubic at 200
dt = DelaunayTri([x(:) y(:)]);

Error in ==> griddata at 136
zi = cubic(x,y,z,xi,yi);

Can you help me with it?

Julie replied on : 21 of 23

Hello,

The code works well, but for relatively small arrays.
I have over 300,000 points, so griddata doesn’t have enough memory to handle the data.
TriScatteredInterp doesn’t work well for me too, because the surface it generates isn’t smooth.

Any suggestions for me?

Traore replied on : 22 of 23

I also have three data colunn, X, Y, Z as:
X Y Z
0.1 0 90
3.5 0 45
4.9 0 65
6.2 0 40
7 0 55
9 0 25
9 5 55
9 3 48
9 7 45
6.5 7 75
4.5 7 50
2.9 7 75
1.3 7 52
0 7 70
0 4.1 90
0 2.1 105
1.7 5.6 75
2.2 4.5 66
2.5 3.6 60
2.9 2.4 55
3.2 1.1 50
1.6 6.6 60
4.7 1 66
4.6 1.6 70
4.5 2.5 80
4.6 3.6 95
4.5 4.2 80
4.3 5.1 70
4.4 6 60
5.3 5.3 78
6 5.7 88
6.9 5.6 102
7.1 5 104
7 3.5 90
6.9 2.7 80
6.9 1.9 70
7 0.6 60
6 1 51
6 2 54
5.9 3 60
6 4 64
6.3 4.8 71
3 6 75
4 4.5 75
5 4.5 73
0.6 5 80
1.8 2 70

Anyone can assist me to plot mesh or surface plot in 3D. Thanks

Reese replied on : 23 of 23

I am also trying to make a 3D plot similar to the the one above. How would I do this if I dont have a function for z.

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