Reverse Polish Notation (RPN) calculator for grids (element by element)
grdmath will perform operations like add, subtract, multiply, and hundreds of other operands on one or more grid files or constants using Reverse Polish Notation (RPN) syntax. Arbitrarily complicated expressions may therefore be evaluated; the final result is written to an output grid file. Grid operations are element-by-element, not matrix manipulations. Some operators only require one operand (see below). If no grid files are used in the expression then options |-R|, |-I| must be set. The expression = outgrid can occur as many times as the depth of the stack allows in order to save intermediate results. Complicated or frequently occurring expressions may be coded as a macro for future use or stored and recalled via named memory locations.
OK, but RPN is quite painfull to master for other than simple expressions and for it the normal Julia operators are much easier to use. However, there are many operators that are handy and already programmed or even kind of unique like for example LDISTG that computes distances to coastlines. So, there is still interest in grdmath but due to its nature it was nor wrapped into a vebose version and for using it one must use the Monolithic mode.
For the full manual, consult the main GMT grdmath manual
To compute all distances to north pole, try::
G = grdmath("-Rg -I1 0 90 SDIST =")
To create a grid with resolution 0.5x0.5 degrees with distances in km from the coast line, use::
G = grdmath("-RNO,IS -Dc -I.5 LDISTG =")