determine if Native grid or not?

Hi All,
I have some questions regarding how to determine if some data is on a
Native grid projection or not, both in general as well as on a particular
grib-file from a mm5-run.

1) From the ncl-manual
http://www.ncl.ucar.edu/Document/Manuals/graphics_man.pdf
I understood that if the file contains an attribute such as "grid type",
it is on Native Grid. Is that correct? Is that always valid?
So, if I run for example ncl_filedump and there is an attribute called
"grid type" it should be on native grid?

2) Running ncl_filedump on my mm5-grib file I get the following:

$ ncl_filedump
DAG/20071112/gribs_d03/gribfile_d3.2007111218.f38.U10SLP.latlon.grib
 Copyright (C) 1995-2007 - All Rights Reserved
 University Corporation for Atmospheric Research
 NCAR Command Language Version 5.0.0
 The use of this software is governed by a License Agreement.
 See http://www.ncl.ucar.edu/ for more details.
Variable: f (file variable)

filename: gribfile_d3.2007111218.f38.U10SLP.latlon
path:
DAG/20071112/gribs_d03/gribfile_d3.2007111218.f38.U10SLP.latlon
   file global attributes:
   dimensions:
      g0_lat_0 = 46
      g0_lon_1 = 69
   variables:
      float PRES_GDS0_GPML ( g0_lat_0, g0_lon_1 )
         center : Athens
         long_name : Pressure
         units : Pa
         _FillValue : -999
         level_indicator : 103
         gds_grid_type : 0
         parameter_table_version : 1
         parameter_number : 1
         level : 0
         forecast_time : 38
         forecast_time_units : hours
         initial_time : 11/12/2007 (18:00)

      float U_GRD_GDS0_HTGL ( g0_lat_0, g0_lon_1 )
         center : Athens
         long_name : u-component of wind
         units : m/s
         _FillValue : -999
         level_indicator : 105
         gds_grid_type : 0
         parameter_table_version : 1
         parameter_number : 33
         level : 10
         forecast_time : 38
         forecast_time_units : hours
         initial_time : 11/12/2007 (18:00)

      float V_GRD_GDS0_HTGL ( g0_lat_0, g0_lon_1 )
         center : Athens
         long_name : v-component of wind
         units : m/s
         _FillValue : -999
         level_indicator : 105
         gds_grid_type : 0
         parameter_table_version : 1
         parameter_number : 34
         level : 10
         forecast_time : 38
         forecast_time_units : hours
         initial_time : 11/12/2007 (18:00)

      float g0_lat_0 ( g0_lat_0 )
         long_name : latitude
         GridType : Cylindrical Equidistant Projection Grid
         units : degrees_north
         Dj : 0.04
         Di : 0.04
         Lo2 : 1.82
         La2 : 40.2
         Lo1 : -0.9
         La1 : 38.4

      float g0_lon_1 ( g0_lon_1 )
         long_name : longitude
         GridType : Cylindrical Equidistant Projection Grid
         units : degrees_east
         Dj : 0.04
         Di : 0.04
         Lo2 : 1.82
         La2 : 40.2
         Lo1 : -0.9
         La1 : 38.4

For example:
for the variable "PRES_GDS0_GPML" there is "gds_grid_type : 0"
and for "float g0_lat_0" there is "GridType : Cylindrical Equidistant
Projection Grid"

a) Is this enough information to tell if it is on Native grid or not?
b) Is it the "float g0_lat_0's GridType" that is important here, or
maybe
"PRES_GDS0_GPML's gds_grid_type" as well?
c) If this file is on a Native Cylindrical Equidistant Projection Grid,
does it matter what kind of mpProjection I use? (as long as I use
'res_at_mpLimitMode = "Corners" ')

Thanks a lot for any advices on this!
/Erik

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Received on Thu Jan 17 2008 - 09:46:06 MST