File Exchange Pick of the Week

November 2nd, 2007

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

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http://blogs.mathworks.com/pick/category/video/

07:30 UTC | Posted in Advanced MATLAB, PodCast, Video | Permalink |

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13 Responses to “Advanced MATLAB: Surface plot of nonuniform data”

1. Masatoshi KASUGA replied on November 18th, 2007 at 20:00 UTC :
   

   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)

2. paul replied on November 19th, 2007 at 07:04 UTC :
   

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

3. Doug replied on November 19th, 2007 at 08:18 UTC :
   

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

   Sorry,
   Doug

4. Doug replied on November 19th, 2007 at 08:22 UTC :
   

   Greg pointed me to this solution he wrote a while back that might be of interest also:

   Tech Note 1212 - Using MESHGRID and GRIDDATA to Fit Vector Data and Plot Unevenly Spaced Data http://www.mathworks.com/support/tech-notes/1200/1212.html

5. Els replied on April 2nd, 2008 at 04:35 UTC :
   

   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

6. Doug replied on April 2nd, 2008 at 10:37 UTC :
   

   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

7. Jim replied on April 3rd, 2008 at 01:33 UTC :
   

   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

8. venkat replied on May 18th, 2008 at 02:47 UTC :
   

   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??

9. Doug replied on May 27th, 2008 at 12:30 UTC :
   

   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

10. Daniel replied on November 8th, 2009 at 21:18 UTC :
    

    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

11. Doug replied on November 10th, 2009 at 15:49 UTC :
    

    @Daniel,

    I think you would be well served to look at the series about volume visualization. It starts here:

    http://blogs.mathworks.com/videos/2009/10/23/basics-volume-visualization-19-defining-scalar-and-vector-fields/

    The one about isosurfaces will be posted today or tomorrow (11/10/2009). That is very likely the function you seek.

    Doug

12. Teja replied on November 11th, 2009 at 13:17 UTC :
    

    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

13. Doug replied on November 11th, 2009 at 20:16 UTC :
    

    @Teja,

    I think this will work:

    http://www.mathworks.com/access/helpdesk/help/techdoc/ref/delaunaytriclass.html

    Doug

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sum(a)
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