# Interpolate to plot contour in plane of non-uniform 3D data

6 views (last 30 days)
Daniel on 17 Jun 2020
Edited: darova on 24 Jun 2020
I have a set of three dimensional data (attached) that is on a non-uniform grid. In the code below, you see how I load, reshape, and plot to get an accurate 3D representation.
clear; close all
node = data(:,2);
orgn = data(:,3);
xr = data(:,4);
yr = data(:,5);
zr = data(:,6);
uu = data(:,7);
vu = data(:,8);
wu = data(:,9);
m = length(orgn(orgn==1)); % the input file is sorted by origin node, so use it to reshape
n = orgn(end);
x = reshape(xr,[m,n]); % each column is a different origin node now
y = reshape(yr,[m,n]);
z = reshape(zr,[m,n]);
u = reshape(uu,[m,n]);
v = reshape(vu,[m,n]);
w = reshape(wu,[m,n]);
quiver3(x,y,z,u,v,w), xlabel('x/R'), ylabel('y/R'), zlabel('z/R')
I've looked around, but I can't figure out how I can create a grid, do some interpolating, and plot a contour slice of this data. For example, how would I plot a contour showing the u data along y = 0 for all x and z?
UPDATE
I got some of it with this:
F = scatteredInterpolant(xr,yr,zr,uu);
[xq,yq,zq] = meshgrid(-1:0.05:8,-1.5:0.5:1.5,-1.5:0.05:1.5);
uq = F(xq,yq,zq);
figure, contourf(squeeze(uq(4,:,:))'), colorbar
The data is new to me, but I think this looks "right". One thing that I'm not getting right is using x and y in contourf to get the axes scaled correctly. I tried contourf(squeeze(xq(4,:,:))',squeeze(yq(4,:,:))',squeeze(uq(4,:,:))'), but this produced a line. I'm missing something... Also, if there are better ways, I'm still interested.
Daniel on 22 Jun 2020

darova on 20 Jun 2020
Edited: darova on 24 Jun 2020
• Use griddata to interpolate your data (create 3d matrices)
• Use slice to create crossection views
x = 2*rand(5000,1)-1;
y = 2*rand(5000,1)-1;
z = 2*rand(5000,1)-1;
v = x.^2 + y.^2 + z.^2;
[xq,yq,zq] = meshgrid(-1:0.1:1);
vq = griddata(x,y,z,v,xq,yq,zq);
plot3(x,y,z,'.r')
slice(xq,yq,zq,vq,[-1 1]/2,[-1 1]/2 ,[])
axis vis3d
Daniel on 23 Jun 2020
I think griddata is the best solution so far. If you'd like to edit your "answer", I can mark it as correct.

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