plotting griddata

Hey All, I was wondering if there was a way to modify the griddata program to include plotting. Given that I am using data points I know I will have to use meshgrid and was trying to figure out how it would be possible to include into the program. Any ideas? Mel

[Walter Roberson]

Why not just call meshgrid() after the griddata() call, as shown in the example in the documentation ?

[Matt Fig]

I think you mean MESH, not MESHGRID.

[Melissa]

As I am trying to implement in a GUI the command window will not be available. When I plug this code into each if statement (ie linear, cubic, nearest) I only receive a plot of the points and not of the generated surfaces. Any suggestions?

%Plotting Griddata

plot3(x,y,z,'o')

hold on

[X,Y]=meshgrid(xi,yi);

surf(X,Y,zi)

hold off

Answer 1

[Matt Fig]

From the doc:

x = rand(100,1)*4-2;  
y = rand(100,1)*4-2;
z = x.*exp(-x.^2-y.^2);
ti = -2:.25:2; 
[XI,YI] = meshgrid(ti,ti);
ZI = griddata(x,y,z,XI,YI);
mesh(XI,YI,ZI), hold
plot3(x,y,z,'o'), hold off

%

%

%

%

EDIT

So do this:

>> edit griddata % Once the file is up, do this:
ctrl+a,ctrl+c,ctrl+n,ctrl+v,ctrl+s  % I recommend using mygriddata

Then look in the new file, and find the last switch statement of the main function. Immediately after that switch statement, put this:

mesh(xi,yi,zi)
hold on 
plot3(x,y,z,'o')
hold off

Or whatever you want.

[Melissa]

Thank you for responding. I understand how to plot in the command window using the examples but I wanted to put inside teh griddata code to plot automatically.

[Walter Roberson]

Melissa, in my experience that is almost certainly the wrong approach to what you are doing.

[Matt Fig]

See my edit above...

[Melissa]

Again thank you so much for taking the time to help me I really appreciate it. I placed it after the switch function given the cases and it produced the error that Z must be a matrix and not a vector or scalar. I don't understand why this works in the command window and not the program itself.

[Matt Fig]

How did you call the new function? Because I called it like this:

x = rand(100,1)*4-2;

y = rand(100,1)*4-2;

z = x.*exp(-x.^2-y.^2);

ti = -2:.25:2;

[XI,YI] = meshgrid(ti,ti);

ZI = mygriddata(x,y,z,XI,YI); % Call new function, made as above

And it worked perfectly. Note that I called the new function.

[Melissa]

I think I am leaving out the meshgrid...hm I wonder if I can place that above the plotting code.

x =[-2 0 1 5 10 6]

y =[-3 7 4 0 3 -1]

z =[-12 7 8 8 4 0]

xi =0:1:10

yi =0:1:10

mygriddata(x,y,z,xi,yi)

[Melissa]

it works perfectly if I use meshgrid in the command window but why cant I use meshgrid within the program itself? I placed it right above the code you have given. Which I very much appreciate and am so thankful for you showing me where to place it.

[Matt Fig]

If you want to be able to call MYGRIDDATA as you did above, put this as the first line of the MYGRIDDATA:

[xi,yi] = meshgrid(xi,yi);

But notice that this will mess up your use of the function the other way... It will indeed be a custom function.

[Melissa]

life saver. thank you.

[Walter Roberson]

I still say it was the wrong approach. If you were going to create a new function, why not create a function that contained the lines I showed and which called the unmodified griddata() ?

[Matt Fig]

That is how I would do it, Walter. But making a custom function from a built-in is o.k. too, I think. I have done so in the past. The thing to avoid is altering the MATLAB version.

Answer 2

[Walter Roberson]

[X,Y] = meshgrid(xi,yi);
Z = griddata(x,y,z,X,Y);
mesh(X,Y,Z), hold
plot3(x,y,z,'o'), hold off

[Melissa]

that only works in the command window.

[Walter Roberson]

Perhaps we are misunderstanding each other, but there is no reason why the code I show above would not work in a script or function, including a callback function.

At most it might be necessary to be more careful about which axes to plot on to.