The execution of gridgen_model.exe is controlled by two user input 
files, wrfsi.nl and input.table, both of which are described below. To 
run gridgen_model, it is only really necessary that the user edit wrfsi.nl
to specify the grid type, the projection and location of the domains, 
the resolution of source data to use for each nest, and the location of
the global static fields. The contents of the input.table file are used
to add additional fields to the output of gridgen_model, or to modify
the way in which any given field is processed by gridgen_model; for 
example, the user may change the interpolation method used with a 
particular field or resolution of source data. Editing input.table is
not necessary if only the default output from gridgen_model is required.

#######################
# wrfsi.nl            #
#######################
wrfsi.nl contains the gridgen_model namelist record, which 
contains variables describing the projection and location of domains.  
The variables in the gridgen_model namelist record are:

 gridtype = {'C', 'E'}  
     the staggering of the model grid.

 max_dom = {INTEGER}    
     the number of domains to be processed; must be <= 20

 parent_id = {INTEGER, 1 to max_dom}  
     the id of this domain's parent; the parent_id of domain 1 is always 1

 parent_grid_ratio = {INTEGER, 1 to max_dom}  
     the ratio of this domain's grid distance to that of it's parent 

 i_parent_start = {INTEGER, 1 to max_dom}  
     the i-coordinate of this domain's left edge in it's parent domain 

 j_parent_start = {INTEGER, 1 to max_dom}  
     the j-coordinate of this domain's bottom edge in it's parent domain 

 s_we = {INTEGER, 1 to max_dom}  
     currently, should be set to 1 for every domain

 e_we = {INTEGER, 1 to max_dom}  
     the size of the west-east dimension for this grid

 s_sn = {INTEGER, 1 to max_dom}  
     currently, should be set to 1 for every domain

 e_sn = {INTEGER, 1 to max_dom}  
     the size of the south-north dimension for this grid

 data_res = {'30s','2m','5m','10m', 1 to max_dom}
     the resolution of source data that should be used when interpolating to 
     this domain

 dx = {REAL}
     for C grid, the nominal grid distance, in meters, of domain 1 in the x 
     direction; for E grid, the delta-longitude, in degrees

 dy = {REAL}
     for C grid, the nominal grid distance, in meters, of domain 1 in the y 
     direction; for E grid, the delta-latitude, in degrees

 map_proj = {'lambert','mercator','polar', 'rotated_ll'}
     the projection of the domains; for E grid, map_proj must be 'rotated_ll'; 
     for C grid, map_proj must not be 'rotated_ll'

 known_x = {REAL}
     for C grid, the i-coordinate of a point in the domain whose lat/lon is 
     known; if not specified, (e_we/2) is assumed

 known_y = {REAL}
     for C grid, the j-coordinate of a point in the domain whose lat/lon is 
     known; if not specified, (e_sn/2) is assumed

 known_lat = {REAL}
     for C grid, the latitude of the point (known_x, known_y); for E grid, the 
     latitude of the point that the origin is rotated to

 known_lon = {REAL}
     for C grid, the longitude of the point (known_x, known_y); for E grid, the 
     longitude of the point that the origin is rotated to

 truelat1 = {REAL}
     for map_proj={'lambert','mercator','polar'}, the first true latitude

 truelat2 = {REAL}
     for map_proj={'lambert'}, the second true latitude

 stand_lon = {REAL}
     for map_proj={'lambert','polar'}, the standard longitude

 io_form_output = {INTEGER}
     the form of the output files written by gridgen_model 

 data_root = {'STRING'}
     the absolute path to the static source fields (i.e., the untarred 
     geog directory)


#######################
# input.table         #
#######################
input.table is a text file that is used to specify which fields 
will be ingested and processed by gridgen_model; it also describes
how each field should be processed by specifying the interpolation 
and smoothing methods to be used for each field. The options that 
may be given in input.table are:

Mandatory options describing what the data is a source of and
when it should be used:
    fieldname = {STRING}  
        name of output field calculated from this source
    output_stagger = {U V M HH VV} 
        the staggering of the output field
    dest_fieldtype = {continuous categorical} 
        type of field calculated from src
    priority = {INTEGER}
        priority level of this source (1 = highest priority)


Options describing other aspects of the source:
    path = {STRING} 
        where to find the data
    fill_missing = {REAL} 
        value assigned to gridpoints that have no data
    halt_on_missing = {yes no}
        halt if missing values found in output field
    z_dim_name = {STRING}
        for 3-d output fields, name of z dimension
    masked = {land water} 
        this is field should be masked by land/water


Option to indicate which field the landmask should be computed from; should be 
specified for exactly one fieldname:
    landmask_water = {INTEGER}
        compute landmask based on value of water
    landmask_land = {INTEGER} 
        compute landmask based on value of land


For dominant category-type fields:
    dominant_category = {STRING}
        name of dominant category to compute from src
    dominant_only = {STRING}
        only compute a dominant category from src

For derivatives (only for continuous fields):
    df_dx = {STRING}
        calculate df_dx for this field, and name the result STRING
    df_dy = {STRING} 
        calculate df_dy for this field, and name the result STRING

Other options:
    scale_factor = {REAL}
        scale final field by this scalar
    interp_option = {sixteen_pt four_pt nearest_neighbor average}
        interpolation type
    smooth_option = {1-2-1 smth-desmth}
        smoothing type, if specified
    smooth_passes = {INTEGER} 
        number of smoothing passes


Mandatory options describing the projection of the source:
These options are actually used in the `index' file for each 
source, NOT in the input.table
    fieldtype = {continuous categorical}
        type of this source data
    proj = {lambert polar mercator regular_ll}
        projection of source
    dx = {REAL}
    dy = {REAL}
    missing_value = {REAL} 
        value of missing data
    signed = {yes no} 
        whether signed in 2's complement format
    known_x = {REAL}
    known_y = {REAL}
    known_lat = {REAL}
    known_lon = {REAL}
    truelat1 = {REAL}
    truelat2 = {REAL}
    stdlon = {REAL}
    units = {STRING}
    description = {STRING}
    wordsize = {INTEGER} 
        how many bytes per value 
    tile_x = {INTEGER}
        number of points in x direction per tile
    tile_y = {INTEGER}
        number of points in y direction per tile
    tile_z = {INTEGER}
        number of points in z direction per tile
    tile_z_start = {INTEGER}
        alternate to tile_z; starting z index
    tile_z_end = {INTEGER}
        alternate to tile_z; ending z index
    tile_bdr = {INTEGER}
        number of halo points around each tile
    category_min = {INTEGER}
        for categorical data, min category in the source
    category_max = {INTEGER}
        for categorical data, max category in the source