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
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DEL
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deletes grids
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GET
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copies grids from one file to another or within the same file
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LIST
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lists grid headers; see the Remarks
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MAKE
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arithmetic operations performed on the grids; see doption and optionn below
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bgrid
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beginning grid number; specify LAST for the last grid in the grid file (default=1)
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egrid
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ending grid number; specify LAST for the last grid in the grid file (default=option dependent; see the Remarks)
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dgrid
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destination grid number; if more than one grid is copied, dgrid is the beginning destination grid number (default=first available)
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sgridf
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source grid file number (default=from IGU SET gridf )
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dgridf
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destination grid file number (default=sgridf )
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grid1 . . n
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a grid number
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doption
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ABV
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creates a grid of absolute vorticity with units 10-5 sec -1; specify the u-component grid as grid1 and the v-component grid with the keyword V; grid2 is ignored
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ADV
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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
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DSH
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creates a deformation shear grid; specify the u-component grid as grid1 and the v-component grid with the keyword V; grid2 is ignored
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DST
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creates a deformation stretch; specify the u-component grid as grid1 and the v-component grid with the keyword V; grid2 is ignored
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DVG
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creates a divergence grid with units 10-6 sec -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
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GEO
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creates u- and v-component grids of the geostrophic wind; specify a height grid as grid1 ; grid2 is ignored
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SPD
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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
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VOR
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creates a grid of vorticity with units 10-6 sec-1; specify the u-component grid as grid1 and the v-component grid in the keyword V; grid2 is ignored
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option1 . . n
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ADD
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adds grids on a point-by-point basis, or adds a constant to a grid; see the Remarks
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AVG
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averages grids on a point-by-point basis
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CHGT
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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
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CHLT
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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
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COM
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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
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COR
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creates a grid of the coriolis force using the grid1 boundaries
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DIV
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divides a grid by another grid or constant; see the Remarks
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FIL
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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
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MPY
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multiplies a grid by another grid or constant; see the Remarks
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RMS
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computes RMS and bias differences of two named grids
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SQR
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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
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SUB
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subtracts a grid from another grid or a constant; see the Remarks
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Keywords
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ADD=
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YES
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corrects for meridional flow; valid only with the derived options ABV, DSH, DVG, VOR, and DST (default)
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NO
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does not correct for meridional flow
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DGRID=
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destination grid number for the MAKE parameter (default=next available grid)
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FORm=
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SHORT
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lists a one-line summary for each specified grid (default)
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ALL
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lists an expanded summary for each grid
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GRIDF=
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grid file number (default=from IGU SET gridf )
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LAB=
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labels the resulting grid (default depends on operation)
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PLANET=
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planet name (default=earth)
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SMO=
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YES
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smooths the resulting grid; only works with the derived options ABV, DVG, VOR, ADB, DST, and DSH (default)
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NO
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does not smooth the resulting grid
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V=
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number of the v-component grid; used with the MAKE option when grid1 is the u-component grid (default=u-grid +1)
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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.
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Column
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Definition
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1
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grid number
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2
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year, Julian day
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3
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hours, minutes and seconds of the grid
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4
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name of the gridded parameter
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5
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description of the atmospheric level and units
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6
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name of the program generating the grid
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7
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hours the forcast grid is valid after generation
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8
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number of rows in the grid
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9
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number of columns in the grid
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10
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latitude and longitude of the upper-left corner
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11
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row grid spacing, in degrees
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12
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column grid spacing, in degrees
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You can use the ADDE commands GRDCOPY and GRDLIST in place of IGG GET and IGG LIST respectively.
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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.
