globalhex runs a DGGRID executable compiled when the package is installed.
To use a different DGGRID build (version 9.0 or later), set
options(globalhex.dggrid = "/path/to/dggrid") or the DGGRID_BIN (or
DGGRID) environment variable. These take precedence over a dggrid on
the PATH, which in turn takes precedence over the bundled copy.