Under-resolved sampling utility

Hi!

I used the command "postProccess -func singleGraph" to extract the boundary layer in a simple lid-driven cavity case with turbulence modeling and a mesh that resolves the boundary layer (y+ of the order of 1). The extracted point clearly missed the near-wall region. I resolved this issue by changing the tolerance in the file $FOAM_SRC/sampling/sampledSet/face/faceOnlySet.C on line 40 to 1e-12. The original line is:

const scalar faceOnlySet::tol = 1e-6;

Therefore, I suggest to modify this value. Perhaps using the SMALL macro would be appropriate? Otherwise, allowing user modification with a lookupOrDefault statement would be nice.

Best regards,

Mathieu Olivier Université Laval

## Reattaching the author to the issue ticket: @mathieu ##