I'm working on a simulation and would like to extract weather data from
grib files.

I'm not very familiar with grib files, but have manged to successfully
compile wgrib.c, and grib2ctl.c However, I'm still in the dark about
how to actually extract what I need from the files.

Which is: wind direction and speed for the nearest given latitude and
longitude.

To this end I would write a function, preferably in ANSI C (with an
eventual port to VB6, and/or VC++).

For example, a prototype of
float get_windspeed(float,float);

With usage like...

windspeed = getwindspeed(latitude,longitude);

I really don't want to reinvent the wheel, and I know there are a few
grib viewers out there that graphically display wind barbs based on
grib data, but what I really need is just the data itself.

I recently obtained a grib file centered at N27, W86 that is suppose to
have wind data for a 100 nm radius. Here's what I get when I run wgrib
and grib2ctl....what do I do with this?

-bash-2.05b$ ./wgrib -V n27w86.grb
rec 1:0:date 2006061512 UGRD kpds5=33 kpds6=1 kpds7=1 levels=(0,1)
grid=233 sfc 24hr fcst: bitmap: 2 undef
UGRD=u wind [m/s]
timerange 0 P1 24 P2 0 TimeU 1 nx 5 ny 7 GDS grid 0 num_in_ave 0
missing 0
center 7 subcenter 0 process 88 Table 0 scan: WE:NS winds(N/S)
latlon: lat 30.000000 to 24.038000 by 1.000000 nxny 35
long -89.000000 to -84.017000 by 1.250000, (5 x 7) scan 0
mode 128 bdsgrid 1
min/max data -6.93 2.23 num bits 8 BDS_Ref -693 DecScale 2
BinScale 2

rec 2:128:date 2006061512 VGRD kpds5=34 kpds6=1 kpds7=1 levels=(0,1)
grid=233 sfc 24hr fcst: bitmap: 2 undef
VGRD=v wind [m/s]
timerange 0 P1 24 P2 0 TimeU 1 nx 5 ny 7 GDS grid 0 num_in_ave 0
missing 0
center 7 subcenter 0 process 88 Table 0 scan: WE:NS winds(N/S)
latlon: lat 30.000000 to 24.038000 by 1.000000 nxny 35
long -89.000000 to -84.017000 by 1.250000, (5 x 7) scan 0
mode 128 bdsgrid 1
min/max data -4.05 2.87 num bits 8 BDS_Ref -405 DecScale 2
BinScale 2


-bash-2.05b$ ./grib2ctl.sh n27w86.grb
dset ^n27w86.grb
index ^n27w86.grb.idx
undef 9.999E+20
title n27w86.grb
* produced by grib2ctl v0.9.12.5p34b
dtype grib 233
options yrev
ydef 7 linear 24.038000 1
xdef 5 linear -89.000000 1.250000
tdef 1 linear 12Z15jun2006 1mo
zdef 1 linear 1 1
vars 2
UGRDsfc 0 33,1,1 ** surface u wind [m/s]
VGRDsfc 0 34,1,1 ** surface v wind [m/s]
ENDVARS




Any help appreciated....I'm stumped.

G