how to convert index of cuda into opencl

hi all

i am new in forum environment and in opencl.
i am very confuse with the get_global_id() like functions

if i have a code on cuda to get the 3d array

    int nBlocksX = nGridPointsX/BLOCK_SIZE;
int nBlocksY = nGridPointsY/BLOCK_SIZE;
int nBlocksZ = nGridPointsZ/BLOCK_SIZE;

dim3 dimGrid(nBlocksX * nBlocksY * nBlocksZ);

    int I = blockIdx.x;
int bx = I%nBlocksX;	
int by = (I/nBlocksX)%nBlocksY;
int bz = I/(nBlocksX*nBlocksY);

int tx = threadIdx.x + bx * BLOCK_SIZE;	
int ty = threadIdx.y + by * BLOCK_SIZE;	
int tz = threadIdx.z + bz * BLOCK_SIZE;

v[tx + tynGridPointsX + tznGridPointsX*nGridPointsY]

how can i convert this code in opencl?
thanks in advance