# 6. Regridding¶

Users that wish to interpolate their unipost output to a different grid may do so with the wgrib2 utility. The general format for re-gridding to various common projections are outlined in the following examples.

Wgrib2 is a versatile program that has the ability to convert grib2 files from one grid to another for various user-defined grids as well as pre-defined NCEP grids. Complete documentation with examples of re-gridding for all available grid definitions can be found at:

## 6.1. Examples of wgrib2¶

Example 1: Latitude-Longitude Grid

-new_grid latlon lon0:nlon:dlon lat0:nlat:dlat outfile

Variable Description
lon0 Longitude of first grid point in degrees
nlon Number of longitudes
dlon Grid resolution in degrees of longitude
lat0 Latitude of first grid point in degrees
nlat Number of latitudes
dlat Grid resolution in degrees of latitude

Example 2: Lambert Conic Conformal Grid

-new_grid lambert:lov:latin1:latin2 lon0:nx:dx lat0:ny:dy outfile

Variable Description
lov Longitude where y axis is parallel to meridian in degrees
latin1 First latitude from pole which cuts the secant cone in degrees
latin2 Second latitude from pole which cuts the secant cone in degrees
lon0 Longitude of the first grid point in degrees
nx Total number of grid points along x
dx Grid cell size in meters in x direction
lat0 Latitude of the first grid point in degrees
ny Total number of grid points along y
dy Grid cell size in meters in y direction

Example 3: Polar Stereographic Grid

-new_grid nps(or SPS):lov:lad lon0:nx:dx lat0:ny:dy outfile

Variable Description
nps/sps North/south polar stereographic
lov Longitude where y axis is parallel to meridian in degrees
lad Latitude where dx and dy are specified
lon0 Longitude of the first grid point in degrees
nx Total number of grid points along x
dx Grid cell distance in meters in x direction at lad
lat0 Latitude of the first grid point in degrees
ny Total number of grid points along y
dy Grid cell distance in meters in y direction at lad

Winds

-new_grid_winds grid(or earth)

Variable Description
grid U-wind goes from grid (i,J) to (i+1,j)
earth U-wind goes eastward, V-wind goes northward

Interpolation

The default interpolation type is bilinear, but it can be set to another type (e.g. neighbor, budget).

-new_grid_interpolation type

Operational Example

Interpolates to a 0.25 degree latitude-longitude grid using various interpolation types depending on the variable.

wgrib2 infile -set_grib_type same -new_grid_winds earth |
-new_grid_interpolation bilinear |
-if ":(CRAIN|CICEP|CFRZR|CSNOW|ICSEV):" -new_grid_interpolation neighbor -fi |
-set_bitmap 1 -set_grib_max_bits 16 |
-if ":(APCP|ACPCP|PRATE|CPRAT):" -set_grib_max_bits 25 -fi |
-if ":(APCP|ACPCP|PRATE|CPRAT|DZDT):" -new_grid_interpolation budget -if |
-new_grid "latlon 0:1440:0.25 90:721:-0.25" outfile


Note: wgrib2 is not distributed within the UFS weather application. Users may download and install from http://www.cpc.ncep.noaa.gov/products/wesley/wgrib2/.