// The 8 children
        // bit2=X,bit1=Y,bit0=Z
        // 0:000: -X -Y -Z
        // 1:001: -X -Y +Z
        // 2:010: -X +Y -Z
        // 3:011: -X +Y +Z
        // 4:100: +X -Y -Z
        // 5:101: +X -Y +Z
        // 6:110: +X +Y -Z
        // 7:111: +X +Y +Z
        NodeBase *pChildren[8];

        // To divide space into 8 octants:
        // Split   on YZ plane into 0,4 (-X in 0, +X in 4)
        // Split 0 on XZ plane into 0,2 (-Y in 0, +Y in 2, -X)
        // Split 4 on XZ plane into 4,6 (-Y in 4, +Y in 6, +X)
        // Split 0 on XY plane into 0,1 (-Z in 0, +Z in 1, -X, -Y)
        // Split 4 on XY plane into 4,5 (-Z in 4, +Z in 5, +X, -Y)
        // Split 2 on XY plane into 2,3 (-Z in 2, +Z in 3, -X, +Y)
        // Split 6 on XY plane into 6,7 (-Z in 6, +Z in 7, +X, +Y)

        // YZ plane vector: 1,0,0
        // XZ plane vector: 0,1,0
        // XY plane vector: 0,0,1

        Node()
        {
            bIsLeaf = FALSE;
        }

        ~Node()
        {
            unsigned i;
            for (i = 0; i < 8; ++i) {
                if (pChildren[i])
                    delete pChildren[i];
            }
        }