How do I use interp3 with grid vectors to interpolate a 3-D int8 array?

I need to resize a 3D int8 array using 'nearest' interpolation. I cannot figure out how to do this for the life of me. I want to use grid vectors, but I can't get them to work. Here is my code...

    voxels(resolution(1),resolution(2),resolution(3))=0; % Not in code. Included for size clarity.

    voxels=interp3(...
        0:(resolution(1)-1),...
        0:(resolution(2)-1),...
        0:(resolution(3)-1),...
        voxels,...
        0:((resolution(1)-1)/(100-1)):(resolution(1)-1),...
        0:((resolution(2)-1)/(104-1)):(resolution(2)-1),...
        0:((resolution(3)-1)/(66 -1)):(resolution(3)-1),...
        'nearest'...
    );

Alternatively I've tried using meshgrid, but the results are the same.

    voxels(resolution(1),resolution(2),resolution(3))=0; % Not in code. Included for size clarity.

    [x,y,z]=meshgrid(...
        0:(resolution(1)-1),...
        0:(resolution(2)-1),...
        0:(resolution(3)-1) ...
    );
    [xq,yq,zq]=meshgrid(...
        0:((resolution(1)-1)/(100-1)):(resolution(1)-1),...
        0:((resolution(2)-1)/(104-1)):(resolution(2)-1),...
        0:((resolution(3)-1)/(66 -1)):(resolution(3)-1) ...
    );
    voxels=interp3(x,y,z,voxels,xq,yq,zq,'nearest');

These both throw the error: The grid vectors do not define a grid of points that match the given values.

When 'nearest' isn't included I get: Sample values must be a single or double array.

Please explain to me what's wrong and how to properly use this function.

[Ken]

Bump.

Answer 1

[Hari]

Hi,

I understand that you're trying to resize a 3D int8 voxel array using 'nearest' interpolation with interp3, and you're encountering errors related to grid compatibility and data types.

I assume that the core issues are:

1. interp3 requires the input array to be of type single or double, not int8.
2. You are mixing up grid vector and full grid (meshgrid) syntax in a way that interp3 does not accept.

In order to resize a 3D array using 'nearest' interpolation with interp3, you can follow the below steps:

Step 1: Convert your voxel array from int8 to double, as required by interp3. This avoids the data type error.

Step 2: If you're using grid vectors (not full meshgrids), you must ensure they are 1D vectors corresponding to each axis, and the dimensions of the data must match [length(y), length(x), length(z)].

Step 3: When defining the query points for interpolation, you must use full 3D grids (i.e., using meshgrid) if you are evaluating on a structured grid. Make sure the axis order matches how interp3 interprets the data.

Step 4: After interpolation, convert the result back to int8 to maintain the original data type.

References:

• https://www.mathworks.com/help/matlab/ref/interp3.html
• https://www.mathworks.com/help/matlab/ref/meshgrid.html

Hope this helps!