View Compilation Error

0_0_21653433_25471.cpp: In member function 'TPoint T3dhull::gracen()':
0_0_21653433_25471.cpp:167:13: 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;
             ^