Introduction

Complex packed grib files can have undefined grid values stored in the grib files as either a bitmap or a special value. You should use the special value method because it results in significantly smaller files. If software is a concern, you should use whatever is compatible with the decoding software. Note: only complex packing allows for using a special value for undefined grid values.

Wgrib2's will store undefined grib values using a special value when using complex packing unless the -set_bitmap 1 option is used. The option -set_grib_type same will not enable the bitmap option.

Software Concerns

NDFD (National Digital Forecast Database) which is produced by NOAA has used complex packing with a special value since the beginning (many years ago). Consequently many decoders will be able to handle special-value undefineds. Many codes will handle bitmaps because bitmaps were used in jpeg2000 packed grib2 files which have been used by NCEP for many years. At least one organization has codes that will not read special-value undefineds.

Usage

-set_bitmap X   X=0, 1   0=do not use bitmap (default) 1=use bitmap
                when packing undefined values with complex packing

Example

$ wgrib2 in.grb -set_bitmap 1 -set_grib_type complex3 -grib_out out.grb 

See also: -grib_out, See also: -set_grib_type,