Error when using isonormals on meshgrid after applying pol2cart

Using the attached data and the following code:

[TH_45, R_45, Z_45] = meshgrid(theta_45,r_45, z_45);
[X_45,Y_45] = pol2cart(TH_45, R_45);
figure;
h = axes;
p1 = patch(isosurface(X_45, Y_45, Z_45,data,500));isonormals(X_45, Y_45, Z_45,data,p1)
p1.FaceColor = 'blue';
p1.EdgeColor = 'none';
view(-23,6); 
axis tight
camlight 
lighting gouraud

I get the following error meassage:

Error using interp3 (line 149) Input grid is not a valid MESHGRID.

Error in isonormals (line 75) n(:,1)=interp3(x, y, z, nx, verts(:,1), verts(:,2), verts(:,3));

I can't find the solution to that issue.

Answer 1

[Anudeep Kumar]

Hey Michael,

I encountered a similar issue when trying to use “isonormals” after applying “pol2cart”. After researching the error and reviewing the documentation, I discovered that the problem arises because the “interpn” function, specifically “interp3” in this case, requires the input values to be strictly monotonic, either increasing or decreasing, across the X1, X2, ..., Xn arrays together. It seems that the “pol2cart” function disrupts this condition.

What worked for me was using the output of the “meshgrid” function directly with “isonormals”. To resolve this, you might first convert your data into Cartesian coordinates and then create the meshgrid, ensuring that the dimensions match. I noticed a dimension mismatch in your data with “theta_45”,” z_45”, and “r_45”. If your use case permits, converting the data to Cartesian coordinates first and then generating the “meshgrid” could resolve the issue

I have attached the link to the latest documentation of interpn:

https://in.mathworks.com/help/matlab/ref/interpn.html

and a MATLAB ANSWER that talks about the same issue:

https://in.mathworks.com/matlabcentral/answers/147483-data-is-not-valid-ndgrid-format

I hope it works for you.