grap
A charting preprocessor for the groff (GNU Troff) document formatting system.
TLDR
Process a grap file and save the output file for future processing with pic and groff
$ grap [path/to/input.grap] > [path/to/output.pic]
Typeset a grap file to PDF using the [me] macro package, saving the output to a file
$ grap [path/to/input.grap] | pic -T [pdf] | groff -[me] -T [pdf] > [path/to/output.pdf]