3d point colouring - 21 by 21 by 21 matrix

Hi,

I have a matrix 21 by 21 by 21. I need to do a "field plot" of this matrix, in which the matrix index defines the position & the value of the matrix element defines the point colour.

Any suggestions how to do this?

Thanks in advance.

Regards,

[Fangjun Jiang]

You could provide a 2x2x2 or 3x3x3 example to better explain what you want.

[Rudra Chattopadhyay]

Suppose

x1 = -2:0.2:2;

x2 = -2:0.25:2;

x3 = -2:0.16:2;

[X1,X2,X3] = ndgrid(x1,x2,x3);

z = X2.*exp(-X1.^2 -X2.^2 -X3.^2);

Here for every z there is a corresponding (X1,X2,X3) & I want a plot with points on the grid coloured according to the value of z.

Answer 1

[Sean de Wolski]

What about something like slice?

doc slice

[Rudra Chattopadhyay]

Thanks for suggesting slice, I'll take help from this one:

% Define 3D data

[x,y,z] = meshgrid(linspace(-1,1,30));

v = x.^2 + y.^2 + z.^2;

% Define the slice plane

[xi, yi] = meshgrid(linspace(-1,1,50));

zi = xi;

% Slice it

slice(x,y,z,v,xi,yi,zi);

I get errors like "size of Z & A should be same" when I use scatter3.

Basically I need to plot a journal bearing parameter like Parasitic torque as the radial clearance, load & r.p.m. varies.

I have vectors for these three. Maybe I'll have to meshgrid these into arrays?

[Sean de Wolski]

That error must be in scatter3 (or have you overwritten the builtin slice?) The above doesn't even call scatter3.

Maybe you could find a picture on google images, a free journal paper, or similar that resembles what you're looking for?

[Fangjun Jiang]

%%

x1 = -2:0.2:2;

x2 = -2:0.25:2;

x3 = -2:0.16:2;

[X1,X2,X3] = meshgrid(x1,x2,x3);

z = X2.*exp(-X1.^2 -X2.^2 -X3.^2);

slice(X1,X2,X3,z,[-1.5 0 1.5],0.8,[-1 0 1])

[Rudra Chattopadhyay]

Thanks a lot, actually I sort of resolved the problem myself when I found a function "isosurface". Was going through an ebook & there various volume visualization functions were given.

I can now plot several isosurfaces with ishold = 1 & put a colorbar.

I think slice too is a good alternative.

[Sean de Wolski]

Don't do it that way Calculate the isosurface once and then plot it with patch(). patch allows for fancy colors and edges/transparencies etc. and the isosurface calculation is computationally expensive so you don't want to do it more times than necessary.

doc isosurface

doc patch

[Rudra Chattopadhyay]

Thanks for the suggestion, will try to use patch() & see the results.

Answer 2

[Image Analyst]

You may need a true volume visualization program like Avizo: http://www.vsg3d.com/avizo/overview. MATLAB can't do anywhere near what Avizo (and similar programs) can do.

[Rudra Chattopadhyay]

Applied for a trial version of Avizo, will see how it goes.