[gradsusr] NWS NDFD grids and GRADS

[Wayne Gibson]

   In attempting to use the temperature National Digital Forecast Grids 
(NDFD) with GRADS, I've found some unexpected results.  If I export the 
grids to ASCII format and read them into another GIS package (GRASS), 
the temperature minimum at a location near Las Vegas are shifted in 
space  westward into California.  The original NDFD grids are in Lambert 
projection GRIB2 format.

My steps are

1) create GRADS control file using g2ctl.pl
2) Created index file using gribmap
3) Run Grads

open temperature.bin.ctl
define newgrid=tmpsfc-273.15
asciigrid newgrid output.asc

4) Import into GRASS, display and compare the geographic locations of 
the temperature minima.

Here are 2 links for graphics showing the apparent shift between the 
GRADS plot and the GRASS GIS plot.

GRADS original: 
http://prism.oregonstate.edu/~gibson/grads/grads_original.png
GRASS shifted: http://prism.oregonstate.edu/~gibson/grads/grass_shifted.png

As you can see, the feature pointed to by the arrows in each plot has 
significantly change location in space.... about 1 degree in longitude.  
I've not reset the dimensions (set x, set y)

Perhaps this is an issue with the way that the National Weather Service 
creates these grids.   Wesley Ebisuzaki has confirmed that the NDFD 
grids are encoded with an unusual scanning mode.  wgrib2 will not work 
with these grids and the "-new_grid" switch.

At this point in time, I'm not sure what other options I have.  I've 
been using this paradigm for years converting NWS Stage IV radar data in 
GRIB1 format to ASCII grids successfully ... no apparent shift in the 
data.  I tried exporting the data using fprintf but had other problems 
(sent a message to the user list a couple days ago).  Somehow I need to 
export the data to an ASCII grid format.

Wayne Gibson
Oregon State University

-------------------
ga-> q config
Config: v2.0.a8.oga.1 little-endian readline printim grib2 netcdf 
hdf4-sds hdf5 opendap-grids,stn athena geotiff shapefile
Grid Analysis and Display System (GrADS) Version 2.0.a8.oga.1
Copyright (c) 1988-2010 by Brian Doty and the
Institute for Global Environment and Society (IGES)
This program is distributed WITHOUT ANY WARRANTY
See file COPYRIGHT for more information.

Built Mon Jul 12 21:25:55 EDT 2010 for i686-pc-linux-gnu

This version of GrADS has been configured with the following options:
   o Built on a LITTLE ENDIAN machine
   o Athena Widget GUI ENABLED
   o Command line editing ENABLED
       http://tiswww.case.edu/php/chet/readline/rltop.html
   o printim command for image output ENABLED
       http://www.zlib.net
       http://www.libpng.org/pub/png/libpng.html
       http://www.libgd.org/Main_Page
   o GRIB2 interface ENABLED
       http://www.ijg.org
       http://www.ece.uvic.ca/~mdadams/jasper
       http://www.nco.ncep.noaa.gov/pmb/codes/GRIB2
       g2clib-1.1.8
   o NetCDF interface ENABLED
       http://www.unidata.ucar.edu/software/netcdf
       netcdf 4.1.1 of Jul 12 2010 21:21:40 $
   o OPeNDAP gridded data interface ENABLED
   o OPeNDAP station data interface ENABLED
       http://iges.org/grads/gadoc/supplibs.html
       libgadap 2.0.oga.1
   o HDF4 and HDF5 interfaces ENABLED
       http://hdfgroup.org
       HDF 4.2r5
       HDF5 1.8.4
   o GeoTIFF and KML output ENABLED
       http://www.libtiff.org
       http://geotiff.osgeo.org
   o Shapefile interface ENABLED
       http://shapelib.maptools.org

For additional information please consult http://iges.org/grads
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