[GRASS-user] r.drain documentation - updated

[Patton, Eric]

Stefano:
>> On the other hand I can't understand why in the man page the section
>> entitled BUG says: "r.drain currently finds only the lowest point
>> (the cell having the smallest category value) in the input file
>> that can be reached through directly adjacent cells that are less
>> than or equal in value to the cell reached immediately prior to it;
>> therefore, it will not necessarily reach the lowest point in the
>> input file. It currently finds pits in the data, rather than the
>> lowest point present.". Why would a local search be a bug in this
>> case? I think it should be like that by design...

Hamish:
>It is like that by design so really a feature not a bug.
>The man page should mention you could fill pits first with a module
>like r.fill.dir or r.terraflow if you want that.
>(the first is listed in the see also section but not explained AFAICS)

I've moved this section from 'Bugs' to 'Notes' to reflect the fact that it is
a feature of the module. There was already mention of using r.fill.dir and 
r.basins.fill for filling local pits, and I've included a mention of r.terraflow
in the 'Notes' section and under 'See Also'.

I added a section in 'Notes' warning the user about running r.drain on region boundary 
points, including the part Maris mentioned from the source code in his post. For now the warning
is under 'Notes', as I didn't really think is was a bug per se, more of a limitation of the module.
I added a hint about using g.region to tweak the region to allow r.drain to find an outlet away from
the region boundary.

~ Eric.