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-set_hex

Introduction

The -set_hex option sets 1 octets (byte) to a a specified hex value. The hex value ranges from 0 to ff.

-set_hex I J K
  I = section number = 1..7
  J = location in the section = 1..(section length)
  K = 00 .. ff
would set
  Section I, Octet J to hex value K

-set_hex I J K1:K2:K3:..KN
  I = section number = 1..7
  J = location in the section = 1..(section length)
  Ki = 00 .. ff

  Sets Section I, Octet J to K1
  Sets Section I, Octet J+1 to K2
  etc

-set_hex I J K1K2K3..KN           for v2.0.8+
  I = section number = 1..7
  J = location in the section = 1..(section length)
  Ki = 00 .. ff
  Sets Section I, Octet J to K1
  Sets Section I, Octet J+1 to K2
  etc

Usage

-set_hex  SECTION STARTING_OCTET_LOCATION (I-1):(I-2):..:(I-N)
-set_hex  SECTION STARTING_OCTET_LOCATION (I-1)(I-2)..(I-N)
SECTION=0 .. 7
OCTET_LOCATION = 1..N
I-M = Mth octet as 2 digit hex number

Example

This examples requires wgrib2 v2.0.8+

The file, template_512.grb, was converted from grib1, and the delta-lon, and the extreme latitudes were only to the nearest millidegree (grib1 precision).

wgrib2 template_512.grb -grid
1:0:grid_template=40:winds(N/S):
    Gaussian grid: (512 x 256) units 1e-06 input WE:NS output WE:SN
    number of latitudes between pole-equator=128 #points=131072
    lat 89.463000 to -89.463000
    lon 0.000000 to 359.233000 by 0.703000

The grid with full precision can be obtained by using -new_grid, and the contents of sec3 (grid definition) can be obtained by -0xSec 3.

-sh-4.1$ wgrib2 template_512.grb -new_grid_winds earth -new_grid ncep grid 170 junk
+ wgrib2 template_512.grb -new_grid_winds earth -new_grid ncep grid 170 junk
1:0:d=2016010109:PRES:mean sea level:2390 hour fcst:
-sh-4.1$ wgrib2 junk -0xSec 3
+ wgrib2 junk -0xSec 3
1:0:Sec3(1..72)=0x0000004803000002000000000028060000000000000000000000000000000000020000000
10000000000ffffffff05551826000000003085551826156a6f6b000aba950000008000

The script to change the precision of the Gaussian grid is given by

sec3='000000480300000200000000002806000000000000000000000000000000000002000000010000000000ffffffff05551826000000003085551826156a6f6b000aba950000008000'
wgrib2 $1 -set_hex 3 1 "$sec3" -grid -grib $1.new

The above script assumes that the size of the original section 3 is greater or equal to the size of the new section 3. If it isn't, you have to use the option -set_sec_size 3 72. Of course, you cannot make arbitrary changes to the grid definition because the number of grid points has to match the grid points in the data section.

See also: -set_byte -set_ieee -set_int -set_int2

Description: misc X Y Z set bytes in Section X, Octet Y, bytes Z (a|a🅱c|abc) in hexadecimal

Docs derived from https://www.cpc.ncep.noaa.gov/products/wesley/wgrib2/set_hex.html