[GRASS-user] r.basin Issues Needing Resolution

[Margherita Di Leo]

Rich,

On Sat, Apr 7, 2012 at 3:51 PM, Rich Shepard <rshepard at appl-ecosys.com>wrote:

> On Sat, 7 Apr 2012, Margherita Di Leo wrote:
>
>  r.basin produces several maps for every run, which are flow direction,
>> accumulation, Horton ordered streams etc.. Prefix parameter is simply a
>> string given by the user in order to distinguish all the maps produced by
>> a
>> single run of the program, i.e. every set of coords for outlet. For
>> example,
>>
>
> madi,
>
>  I thought this is the case, but wanted to know rather than assume.
>
>
>  Threshold parameter is the same of r.watershed. 'Autothreshold ' flag'
>> simply uses a threshold area of 1 km^2 and is intended as a tentative.
>>
>
>  Again, rather than assuming I wanted to be sure I understood.
>
>
>  For what concerns r.stream.basin, it is a typo in the documentation,
>> correct is r.stream.basins, thanks for pointing me out, I just updated it
>> in the description file.
>> r.wf.py and r.ipso.py are in the addOns repository:
>>
>
>  Ah, I see why they did not download for me: I added the .py extention to
> the g.estension command. Now I know to leave it off.
>
>
>  Please note that r.basin is intended to work with only one outlet at time.
>> This means you should script it in a for cycle if you run it for several
>> outlets.
>>
>
>  I understand this.
>
>
>   You can't give to r.basin the coordinates directly from a vector map.
>>
>
>  But, can I use the coordinates of a rasterized stream network?


No. Do you think this would be an useful add? If so, I could work on it
when I have some spare time.. Let me know.

>
>
>  I have indicated to run r.stream.extract before r.basin because most of
>> the
>> times the calculated stream network doesn't match with the natural one, so
>> that your coordinates should be adjusted to match the calculated stream
>> network in order to get a result from r.basin. By the way, in a first run
>> you can give a try with your coordinates.
>>
>
>  The outputs of r.stream.extract on two different project sub-watersheds
> are, as far as I can see on the display, only about 5-10% of the vector
> stream network, and all at the lower ends of the basins in which they
> appear. I can send screen shots if you'd like to see the differences.
>

AFAICT this could be due to an odd value for the threshold, or a g.region
or mask related problem. Please try setting g.region to match the elevation
map, removing the mask and setting a lower threshold value.

>
>  After downloading and building the 'missing' three modules I'll try
> v.to.rast on the natural stream network (at 1:24,000 scale, just like the
> elevation data) and see what r.basin tells me.
>

Let me know about your results.

madi

>
> Many thanks,
>
>
> Rich
>
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-- 
Ing. Margherita Di Leo, Ph.D.
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