Contourslice error

I keep getting the following error and I can't figure out why:

??? Error using ==> interp3 at 138 X, Y and Z must be matrices produced by MESHGRID. Use TriScatteredInterp instead of INTERP3 for scattered data.

Error in ==> contourslice at 124 vi = interp3(x, y, z, v, xi, yi, zi, method);

Error in ==> MagPlot at 21 contourslice(xg, yg, zg, maginterp,[],[],-0.4,20);

This is the associated script (x, y and z are vectors and mag is an array of several sets of data at x,y and z):

load('mag.mat'); coords=xlsread('NodeCoords.xls'); nodenum=coords(:,1); x=coords(:,2); z=coords(:,3); y=coords(:,4); clear coords

r=0:0.01:1; theta=0:pi/50:2*pi; zg=-0.45677:(-0.38877+0.45677)/9:-0.38877; [r,theta,zg]=meshgrid(r,theta,zg); xg=r.*cos(theta); yg=r.*sin(theta);

F=TriScatteredInterp(x,y,z,mag(:,1,700)); maginterp=F(xg,yg,zg); contourslice(xg, yg, zg, maginterp,[],[],-0.4,20);

[Sean de Wolski]

Good question (though you need to edit the code formatting)! +1 for being interesting.

Answer 1

[Sean de Wolski]

[r,theta,zg]=meshgrid(r,theta,zg);
xg=r.*cos(theta); 
yg=r.*sin(theta);

When you multiply xg,yg by the sine and cosine of theta they lose their meshgrid-like properties (i.e. monotonicity) and their corresponding signs.

A good way to visualize this to look at the contour of the first slice of xg:

contour(xg(:,:,1))