Hi Mark,
You could do the following:
Using GDINFO output, identify the GFUNC, GLEVEL, GVCORD of interest. For
example, using today's 0Z GFS grid I do the following:
GDFILE = gfs_3_20091116_0000_006.grd
LSTALL = YES
OUTPUT = T
GDATTIM = all
GLEVEL = all
GVCORD = all
GFUNC = all
GEMPAK-GDINFO>r
I'm interested in RELH at 800, 700, 600, and 500 mb in New York City, NYC
(40.783, -73.883). Within the GDINFO output I see:
100 091116/0000F006 800 PRES RELH
116 091116/0000F006 700 PRES RELH
132 091116/0000F006 600 PRES RELH
148 091116/0000F006 500 PRES RELH
Using GDPOINT, pull the RELH values of interest:
gdpoint
GDATTIM = 091116/0000F006
GDFILE = gfs_3_20091116_0000_006.grd
GLEVEL = 800
GPOINT = 40.783;-73.883
GVCORD = PRES
GFUNC = RELH
SCALE = 0
GEMPAK-GDPOINT>r
GDFILE: gfs_3_20091116_0000_006.grd
GPOINT: 40.783;-73.883
GVCORD: PRES
GLEVEL: 800
GFUNC : RELH
SCALE : 0
091116/0000F006 : 58.81023
Parameters requested: GDATTIM,GDFILE,GLEVEL,GPOINT,GVCORD,GFUNC,SCALE.
GEMPAK-GDPOINT>GLEVEL=700
GEMPAK-GDPOINT>r
GDFILE: gfs_3_20091116_0000_006.grd
GPOINT: 40.783;-73.883
GVCORD: PRES
GLEVEL: 700
GFUNC : RELH
SCALE : 0
091116/0000F006 : 27.16799
Parameters requested: GDATTIM,GDFILE,GLEVEL,GPOINT,GVCORD,GFUNC,SCALE.
GEMPAK-GDPOINT>GLEVEL=600
GEMPAK-GDPOINT>r
GDFILE: gfs_3_20091116_0000_006.grd
GPOINT: 40.783;-73.883
GVCORD: PRES
GLEVEL: 600
GFUNC : RELH
SCALE : 0
091116/0000F006 : 8.15741
Parameters requested: GDATTIM,GDFILE,GLEVEL,GPOINT,GVCORD,GFUNC,SCALE.
GEMPAK-GDPOINT>GLEVEL=500
GEMPAK-GDPOINT>r
GDFILE: gfs_3_20091116_0000_006.grd
GPOINT: 40.783;-73.883
GVCORD: PRES
GLEVEL: 500
GFUNC : RELH
SCALE : 0
091116/0000F006 : 3.61722
GDPOINT uses the 8 closest GRID points to calculate an interpolated value at
the LAT/LON you request. Using 8 points could be an issue with coarser
models as the interpolation would include grid points far removed from your
LAT/LON point.
Regards,
Evan
Business Applications Meteorologist
Weather Trends International, Inc.
Phone 610-807-3197
http://www.wxtrends.com
-----Original Message-----
From: gembud-bounces@xxxxxxxxxxxxxxxx
[mailto:gembud-bounces@xxxxxxxxxxxxxxxx] On Behalf Of Mark Hughes
Sent: Tuesday, November 17, 2009 12:48 PM
To: gembud@xxxxxxxxxxxxxxxx
Subject: [gembud] Interpolating levels in GRIB data
Hi All,
I am working with models produced from wind and temperature GRIB data.
(DCGRIB2 produces a .gem model from HT*, HU* and HV* messages).
I am trying to extract point data using GDPOINT at an arbitrary level.
Can anyone tell me how to interpolate? Or, as an alternative, how can I
create a new grid with finer resolution in the level dimension?
Many thanks,
Mark Hughes
Global Weather Dynamics
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