View Compilation Error

0_0_37011538_31775.cpp: In member function 'TPoint T3dhull::gracen()':
0_0_37011538_31775.cpp:167:22: error: 'hull' was not declared in this scope
             double v=hull.volume(po,ply[tri[i].a],ply[hull.tri[i].b],ply[tri[i].c])/6.0;
                      ^