In Grass r.watershed the D8 drainage directions generated from r.watershed are -8. -6.-4.-2, 2, 4, 6, 8 (-1 No Data)

**What actual directions are these?**

For example in ArcGIS I know 128 is up and so on from this diagram.

[![enter image description here](https://i.stack.imgur.com/6uPLs.gif)](https://i.stack.imgur.com/6uPLs.gif)

**What in Grass r.watershed which is up, right, etc?**

When I compare the value to ArcGIS it would be

r,waterhsed (grass).....ArcGIS (flow).....Direction

8 ..........................................1.....................East

6 ..........................................4.....................South

4 .........................................16.....................West

2 .........................................64.....................North

The minus value are very few and likely edge pixel as the grass manual states.

**But I would like a source to confirm this (and why only 8 values?)**