I'm not familiar with scikit-image. I  only want to use the function `measure.marching_cubes`,
but I cannot figure out what really represent the values returned by it.

`help(measure.marching_cubes)` says:

values : (V, ) array
Gives a measure for the maximum value of the data in the local region
        near each vertex. This can be used by visualization tools to apply
        a colormap to the mesh.

What is data here (this term is too general)? 
I saw that values.shape[0] is the same as vertices.shape[0]. Hence each value is associated to a vertex.
 How is it assigned to a vertex? How are these values related to the volume or to the equation F(x,y,z)=0? 
(I want to extract a triangulation of an implicit surface having this equation).

A second question is related to the coordinates of vertices.
When I plot the  trisurf defined by `vertices` and `faces` I notice 
that the x, y and z-range illustrated by tick values
is different from the real values. More precisely: if my surface has zmin=-1 and zmax=2,  on z-axis
this range is [5,11].  Is there a transformation that maps the vertices coordinates, as they are returned by 
`measure.marching_cubes` to real coordinates on my surface?