Plot a 3D matrix for a three-dimensional object

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Yuzhen Lu
Yuzhen Lu 2017-2-11
评论： DGM 2023-3-22
I have obtained a 3D matrix A(:,:,3) for the geometry of an object. A(:,:,1) is a matrix corresponding to x coordinates in the world coordinate system, and A(:,:,2) stores y coordinates and A(:,:,3) stores the z coordinates. So each point the object has three coordinates (x,y,z). It is noted that these coordinates are scattered, and some of them are non-integer.
Now I am going to plot the 3D surface or shape of the object. I am wondering what Matlab function or functions are best or suitable for the purpose.
A possible way is to use plot3 as follows:
x = A(:,:,1);
y = A(:,:,2);
z = A(:,:,3);
figure; plot3(x,y,z,'.-'); %the figure is attached below
But this function does not give a desired figure. less authentic, no shading or camlight functions supported. trisurf.m seems a good choice for the problem. Are there any other options?

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回答（5 个）

Chad Greene
Chad Greene 2017-2-11
编辑：Chad Greene 2017-2-11
Hi Yuzhen,
Are the x and y values evenly spaced, or are they randomly scattered about? If the x and y values are evenly spaced, you can use xyz2grid.
[X,Y,Z] = xyz2grd(A(:,1),A(:,2),A(:,3));
surf(X,Y,Z)
shading flat
camlight
But if the data points are scattered, you'll have to grid them with one of the scattered interpolation functions. My go-to gridding function is John D'Errico's gridfit, which is on File Exchange.
  2 个评论
Yuzhen Lu
Yuzhen Lu 2017-2-11
Thanks for your answer!
These coordinates are not evenly spaced, and some of them are non-integer. I will try your suggestion
Chad Greene
Chad Greene 2017-2-12
Are you sure there's no regularity to the x and y spacing? It's hard to tell in your plot, but it looks like there might be some common intervals. It's fine is some of them aren't integers, you can still use xyz2grid. I try to avoid any kind of grid fitting if the data are already gridded but inconveniently formatted.

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Swati Jain
Swati Jain 2020-3-27
For future if someone come across same issue:
One can use pchow
https://www.mathworks.com/help/vision/ref/pcshow.html
and scatter3
https://www.mathworks.com/help/matlab/ref/scatter3.html
You can see shading with scatter3 by using the follwoing:
scatter3(x, y, z,[],z, '.')
Arjun Tandon
Arjun Tandon 2019-7-26
I don't have the xyz2grd function, so I've done it this way. It's not pretty, but it's worked for me.
%% Cleaning up
clc
clear
close
%% Generating 3D data
for i = 1:100
for j = 1:100
for m = 1:100
A(i,j,m) = i+j+m;
end
end
end
%% This is the important part. Here, I'm just extracting the
%% vector data and storing it in variables.
X = A(:,1);
Y = A(:,2);
Z = A(:,3);
T = [X,Y,Z]; %Creating a matrix (10 by 10 by 10)
%% Graphical bits
surf(T)
shading flat
me. Hypothetically, you could also modify Chad's method (shown below); I was too lazy to try.
T = [A(:,1), A(:,2), A(:,3)];
Nilar Htun
Nilar Htun 2020-9-2
编辑：DGM 2023-3-22
x = A(:,:,1);
y = A(:,:,2);
z = A(:,:,3);
[x, y, z] = meshgrid(A(:,1), A(:,2), A(:,3));
surface(x,y,z);
figure;
scatter3(x,y,z,'.-');
figure;
shading flag
  1 个评论
DGM
DGM 2023-3-22
This appears to be a nonfunctioning collage of copy-pasted code.
% so A is a 3D array with at least 3 pages
% now x,y,z are 2D arrays corresponding to those pages
x = A(:,:,1);
y = A(:,:,2);
z = A(:,:,3);
% throw all that away and sample the first three
% columns of the first page of A instead.
% now x,y,z are all 3D arrays
[x, y, z] = meshgrid(A(:,1), A(:,2), A(:,3));
% surface(), surf(), scatter3() do not accept 3D arrays
% surface()/surf() work with gridded data
% which wasn't what the original problem had
surface(x,y,z);
figure; % normally you create a figure _before_ you use it
scatter3(x,y,z,'.-');
figure;
% there is no such option for shading
% either this is supposed to be
% shading flat
% or
% colormap(flag)
shading flag
What's the point of posting this?

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wang zhiming
wang zhiming 2023-3-22
编辑：DGM 2023-3-22
Ran in:
rng(9,'twister')
data = rand(10,10,10);
data = smooth3(data,'box',5);
patch(isocaps(data,.5),...
'FaceColor','interp','EdgeColor','none');
p1 = patch(isosurface(data,.5),...
'FaceColor','blue','EdgeColor','none');
isonormals(data,p1)
view(3);
axis vis3d tight
camlight left;
colormap jet
lighting gouraud

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