McIDAS-X User's Guide
Version 2021.1
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IGG
Grid
utility.
Formats
IGG
DEL bgrid egrid GRIDF=
IGG GET sgridf bgrid egrid dgridf dgrid
IGG LIST bgrid egrid FORM=
GRIDF=
IGG MAKE grid1 doption grid2 [keywords]
IGG MAKE grid1 option1 . . gridn
optionn [keywords]
Parameters
DEL |
deletes
grids |
GET |
copies
grids from one file to another or within the same file |
LIST |
lists
grid headers; see the Remarks |
MAKE |
arithmetic
operations performed on the grids; see doption and optionn below |
bgrid |
beginning
grid number; specify LAST for the last grid in the grid file (default=1) |
egrid |
ending
grid number; specify LAST for the last grid in the grid file (default=option
dependent; see the Remarks) |
dgrid |
destination
grid number; if more than one grid is copied, dgrid is the beginning
destination grid number (default=first available) |
sgridf |
source
grid file number (default=from IGU SET gridf) |
dgridf |
destination
grid file number (default=sgridf) |
grid1 . . n |
a
grid number |
doption |
ABV |
creates
a grid of absolute vorticity with units 10-5sec-1;
specify the u-component grid as grid1 and the v-component grid
with the keyword V; grid2 is ignored |
|
ADV |
creates
an advection grid of the grid2 parameter in units/day; specify
the u-component grid as grid1 and the v-component grid with
the keyword V |
|
DSH |
creates
a deformation shear grid; specify the u-component grid as grid1 and
the v-component grid with the keyword V; grid2 is ignored |
|
DST |
creates
a deformation stretch; specify the u-component grid as grid1 and
the v-component grid with the keyword V; grid2 is ignored |
|
DVG |
creates
a divergence grid with units 10-6sec-1; specify
the u-component grid as grid1 and the v-component grid with
the keyword V; if grid2 is
specified, the divergence of its parameter is computed |
|
GEO |
creates
u- and v-component grids of the geostrophic wind; specify a height grid
as grid1; grid2 is ignored |
|
SPD |
creates
a grid of wind speed; specify the u-component grid as grid1 and
the v-component grid with the keyword V; grid2 is ignored |
|
VOR |
creates
a grid of vorticity with units 10-6sec-1; specify
the u-component grid as grid1 and the v-component grid in the
keyword V; grid2 is
ignored |
option1 . . n |
ADD |
adds
grids on a point-by-point basis, or adds a constant to a grid; see the
Remarks |
|
AVG |
averages
grids on a point-by-point basis |
|
CHGT |
changes
all input grid points with values greater than the specified constant
to that constant in the output grid; grid points with values less than
the constant are not changed; see the Remarks |
|
CHLT |
changes
all input grid point values less than the specified constant to that
constant in the output grid; grid points with values greater than the
constant are not changed; see the Remarks |
|
COM |
compares
two grids for overlapping values; for a threat score, the second grid
should be followed by two numbers that specify the range of values to
include, for example, MAK 12 COM 18 -500 500 |
|
COR |
creates
a grid of the coriolis force using the grid1 boundaries |
|
DIV |
divides
a grid by another grid or constant; see the Remarks |
|
FIL |
creates
a grid with the specifications of the first grid but fills it with the
value specified for the second grid, for example, MAK 12 |
|
MPY |
multiplies
a grid by another grid or constant; see the Remarks |
|
RMS |
computes
RMS and bias differences of two named grids |
|
SQR |
square
root; applies to the first grid only; it can be used with any two successive
grids to reproduce a grid of the square root of the sum of the squares |
|
SUB |
subtracts
a grid from another grid or a constant; see the Remarks |
Keywords
ADD= |
YES |
corrects
for meridional flow; valid only with the derived options ABV, DSH, DVG,
VOR, and DST (default) |
|
NO |
does
not correct for meridional flow |
DGRID= |
destination
grid number for the MAKE parameter (default=next available grid) |
FORm= |
SHORT |
lists
a one-line summary for each specified grid (default) |
|
ALL |
lists
an expanded summary for each grid |
GRIDF= |
grid
file number (default=from IGU SET gridf) |
LAB= |
labels
the resulting grid (default depends on operation) |
PLANET= |
planet
name (default=earth) |
SMO= |
YES |
smooths
the resulting grid; only works with the derived options ABV, DVG, VOR,
ADB, DST, and DSH (default) |
|
NO |
does
not smooth the resulting grid |
V= |
number
of the v-component grid; used with the MAKE option when grid1 is
the u-component grid (default=u-grid +1) |
Remarks
When using
LIST, egrid's default is bgrid. If you do not specify bgrid and egrid, egrid's
default is LAST if FORM=SHORT and bgrid if FORM=ALL. When using DEL
or GET, egrid's default is bgrid.
To apply a
constant to an arithmetic function (ADD, DIV, MPY, SUB), enter a negative number
for the second named grid. The absolute value of this number is used
as a constant.
In the CHLT
and CHGT options, the number specified for the second named parameter (gridn)
is used as a constant. Input grid point values less than (CHLT option) or greater
than (CHGT option) this constant are changed to the constant in the output
grid. See the last example.
Grids created
using IGG MAKE and those created using GRDCOPY with the DERIVE or MATH keyword
may not yield numerically identical results. However, the values for both are
correct. The differences are the result of one of the following:
- By default,
IGG MAKE applies a smoothing function and, if applicable, a meridional correction
term to the data. GRDCOPY does not do this by default. You can override the
IGG MAKE defaults by specifying SMO=NO and ADD=NO.
- Grids
created using GRDCOPY will be in Standard International units, whereas grids
created using IGG MAKE may not be. For example, a grid created using the
TADV (temperature advection) function in IGG MAKE will be in degrees per
day, while a similar grid created using GRDCOPY with the MATH keyword will
be in degrees per second unless a factor is added to the equation to compute
it in degrees per day.
The output
of command IGG LIST contains the information below.
| Column |
Definition |
| 1 |
grid
number |
| 2 |
year,
Julian day |
| 3 |
hours,
minutes and seconds of the grid |
| 4 |
name
of the gridded parameter |
| 5 |
description
of the atmospheric level and units |
| 6 |
name
of the program generating the grid |
| 7 |
hours
the forcast grid is valid after generation |
| 8 |
number
of rows in the grid |
| 9 |
number
of columns in the grid |
| 10 |
latitude
and longitude of the upper-left corner |
| 11 |
row
grid spacing, in degrees |
| 12 |
column
grid spacing, in degrees |
You can use the ADDE commands GRDCOPY
and GRDLIST
in place of IGG GET and IGG LIST respectively.
|
See Also
See commands GRDDISP and MDX to
plot and contour grid point values.
Examples
IGG LIST
This entry
lists all the grids in your workstation's default grid file.
IGG LIST 1 20
This entry
lists all grids from 1 to 20 from the default grid file.
IGG DEL
This entry
deletes grid one in the default grid file.
IGG GET 10 5 7 20 1
This entry
moves grids 5, 6 and 7 from grid file 10 into grid file 20, starting at grid
1, or the next available grid.
IGG MAKE 2 SUB 1
This entry
creates a new grid by subtracting grid 1 from grid 2.
IGG MAKE 2 MPY -4 ADD 5 DIV -60
This entry
creates a new grid by multiplying each grid point in grid 2 by the constant
4, adding them to grid 5 and dividing by the constant 60.
IGG MAKE 100 CHLT 273
This entry
creates a new grid by checking each grid point value in grid 100 and changing
all grids point values less than 273 to 273. The grid points with values greater
than 273 are not changed.
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