I have to do some geometrical calculations in 2D(point, lines, line segments and intersection points) in Python, and then use it in GRASS GIS. What is the best library to use for it? I'm trying with SymPy, but I'm not sure is that good choice.
Sympy is inappropriate here (or very difficult to use). For geometrical calculations in 2D, the best solution is Shapely.
After, it is possible to mix all as in GRASS and the Python geospatial modules (Shapely, PySAL,...)