Isovalue in Matlab's Isosurface

As I read the Matlab help, the isosurface() takes the form of

fv = isosurface(V,isovalue)

V is the volume data,

I think a isosurface should plot the surface have the value of isovalue. However, as I tried myself, it looks like Matlab plots all the points with value > isovalue.

This is so confusing. Is this isovalue actually a threshold value?!

Thanks a lot!

isosurface does no plotting. It computes the isosurface geometry some data at the given isovalue.

The output contains the faces and verticies of the isosurface that can be passed directly to patch.

You should do help isosurface for an explanation as well as two examples on how it's used.

You'll have to include more code for more help, since you can't possibly be plotting anything with the command that you wrote.