bedGraphToBigWig usage

bedGraphToBigWig v 4 - Convert a bedGraph file to bigWig format.
usage:
   bedGraphToBigWig in.bedGraph chrom.sizes out.bw
where in.bedGraph is a four column file in the format:
      <chrom> <start> <end> <value>
and chrom.sizes is two column: <chromosome name> <size in bases>
and out.bw is the output indexed big wig file.
Use the script: fetchChromSizes to obtain the actual chrom.sizes information
from UCSC, please do not make up a chrom sizes from your own information.
The input bedGraph file must be sorted, use the unix sort command:
  sort -k1,1 -k2,2n unsorted.bedGraph > sorted.bedGraph
options:
   -blockSize=N - Number of items to bundle in r-tree.  Default 256
   -itemsPerSlot=N - Number of data points bundled at lowest level. Default 1024
   -unc - If set, do not use compression.