As far as I checked, even when you set initial value inside the class, you still need to define it in body file. I mean,
```
const unsigned Face::Dimension;
```
in Face.cpp

Therefore I decided to write the initial value in cpp file. see
http://stackoverflow.com/questions/4547660/c-static-member-variable-and-its-initialization
http://stackoverflow.com/questions/2605520/c-where-to-initialize-static-const