Aside from using
r.fill.dir in GRASS, is this the script to produce the Flow or directional raster map? Is the output for the script the following graphic? http://grass.fbk.eu/grass63/screenshots/images/drastarrow.png
We're looking for long answers that provide some explanation and context. Don't just give a one-line answer; explain why your answer is right, ideally with citations. Answers that don't include explanations may be removed.