GRDMATH

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NAME

grdmath - Reverse Polish calculator for grd files  

SYNOPSIS

grdmath [ -Ixinc[m|c][/yinc[m|c]] -Rwest/east/south/north -V] operand [ operand ] OPERATOR [ operand ] OPERATOR ... = outgrdfile  

DESCRIPTION

grdmath will perform operations like add, subtract, multiply, and divide on one or more grd files or constants using Reverse Polish syntax (e.g., Hewlett-Packard calculator-style). Arbitrarily complicated expressions may therefore be evaluated; the final result is written to an output grd file. When two grd files are on the stack, each element in file A is modified by the corresponding element in file B. However, some operators only require one operand (see below). If no grdfiles are used in the expression then options -R, -I must be set (and optionally -F).
operand
If operand can be opened as a file it will be read as a grd file. If not a file, it is interpreted as a numerical constant or a special symbol (see below).
outgrdfile is a 2-D grd file that will hold the final result.
OPERATORS
Choose among the following operators:
Operator               n_args  Returns

#include "grdmath_man.i"

SYMBOLS
The following symbols have special meaning:

PI     3.1415926...

E      2.7182818...

X      Grid with x-coordinates

Y      Grid with y-coordinates

 

OPTIONS

-I
xinc [and optionally yinc] is the grid spacing. Append m to indicate minutes, c to indicate seconds. #include "explain_-R.txt"
-F
Select pixel registration. [Default is grid registration]. #include "explain_-V.txt"
 

EXAMPLES

To multiply test.grd by 10.0, try
       grdmath test.grd 10.0 MUL = test10.grd

To take log10 of the average of 2 files, use
       grdmath file1.grd file2.grd ADD 0.5 MUL LOG10 = file3.grd

Given the file ages.grd, which holds seafloor ages in m.y., use the relation depth(in m) = 2500 + 350 * sqrt (age) to estimate normal seafloor depths:
       grdmath ages.grd SQRT 350 MUL 2500 ADD = depths.grd

To find the angle a (in degrees) of the largest principal stress from the stress tensor given by the three files s_xx.grd s_yy.grd, and s_xy.grd from the relation tan (2*a) = 2 * s_xy / (s_xx - s_yy), try
       grdmath 2 s_xy.grd MUL s_xx.grd s_yy.grd SUB DIV ATAN2 2 DIV = direction.grd
 

BUGS

Files that has the same name as some operators, e.g., ADD, SIGN, =, etc. cannot be read and must not be present in the current directory. Piping of files are not allowed. The stack limit is hard-wired to 50.  

SEE ALSO

gmt, grd2xyz, grdedit, grdinfo, xyz2grd #include "refs.i"


 

Index

NAME
SYNOPSIS
DESCRIPTION
OPTIONS
EXAMPLES
BUGS
SEE ALSO

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Time: 07:11:10 GMT, January 07, 2025