p2cgrb | c2pgrb - GRIB polar to Cartesian converters
p2cgrb & c2pgrb convert GRIB records
from polar (magnitude & direction) to east and north components and
vice versa.
Comments are appreciated, future versions may appear.
Syntax
% p2cgrb speed.grb dir.grb uv.grb [[-]u-par v-par]
% c2pgrb u.grb v.grb polar.grb [[-]magnitude-par
dir-par]
Here, the two first grib files are input files containing matching
magnitude and direction records or east and north component records,
respectively for p2cgrb
and c2pgrb. The optional
parameters at the end of the argument list indicate which parameters
numbers the new fields should be given. This is optional, if left out,
the standard parameter numbers for wind speed and wind direction or
east and north components of the wind are used (parameters 31-34 in the
standard table).
Facts & caveats
- The angle is assumed to be in degrees clockwise from north, in
the
direction from which the vector is pointing, i.e., the "coming-from" or
meteorological convention. To revert this, add a negative sign to
either of the two parameters at the end of the argument list (see
examples below).
- Vector components near the poles should be handled with care
- Vector components are assumed to be in east and north direction,
hence the code should not be used with components pointing along the
local direction of the grid
Examples
-
p2cgrb speed.grb dir.grb uv.grb -49 50
The new file uv.grb
contains the east and north components of the surface current vector
with parameter nos 49 and 50 [optional, default 33 and 34]. Direction
is assumed to be in the "going-to" or oceanographic
convention (note the negative sign on parameter 49).
-
c2pgrb u.grb v.grb polar.grb -48 47
The new file polar.grb
contains the speed and direction of the surface current vector with
parameter nos 48 and 47 [optional, default 32 and 31] .
Again, direction is in the "going-to" or oceanographic convention (note
the negative sign on parameter 48).
Installation
% gunzip p2c.tar.gz
% cd Gribw
% make -f gribwlib.make
% cd ../P2cgrb
% make -f p2cgrb.make p2cgrb
% make -f p2cgrb.make c2pgrb
The TAR-ball includes a Linux binary of bilingrb, which
makes compilation unnecessary for those fortunate owners of Linux
boxes. Four test files are also included (speed.grb, dir.grb, u.grb, and v.grb).
See also
- ggrib, a
program for
extracting subdomains without interpolating
- bilingrb, a program
for extracting subdomains with interpolation or subsampling (e-mail me
for a copy)
- wgrib, a
program for
viewing and extracting records
v1.0, 2004m08d05,
oyvind.breivik@met.no
--
Øyvind Breivik, Norwegian Meteorological Institute,
www.met.no