[GRASS-user] r.basins.fill usage

[MS]

Thanks to all for the help and guidence.

Mark

On Oct 16, 2009, at 6:20 AM, Jarosław Jasiewicz <jarekj at amu.edu.pl>  
wrote:

> Hi
> try r.stream.basins from grass add-ons it has options (-c and -l  
> flags) to generate subbasin without any manual work. Look also into  
> tutorial on grass wiki about it (wiki -> dokuments ->r.stream.*
>
> Jarek
> Achim Kisseler pisze:
>>> Based on this excerpt from the manual, it seems the main
>>> external/perimeter watershed boundary, as well as the internal  
>>> ridges
>>> need inputted?  "The raster map layer depicting ridges should  
>>> include
>>> the ridge which defines the perimeter of the watershed. The coded
>>> stream network can be generated as part of the r.watershed program,
>>> but the map layer of ridges will need to be created by hand"
>>>
>>> My question is really about the need to manually digitize ridges
>>> inside the watershed boundary delineated by r.watershed.  As opposed
>>> to running r.watershed with a smaller threshold to get these smaller
>>> basin delineations within a given study area.
>>>
>>> If one has to manually digitize the internal ridges in a  
>>> watershed, I
>>> wondered what the point of the module was.  It obviously has
>>> application, but it seems I am missing something obvious.
>>>
>>> Hope that is more clear.
>>>
>>
>> Now its much clearer to me. Thanks.
>>
>> In my opinion the description ao r.basins.fill is now very  
>> detailed. I
>> don't really understand it. So maybe someone else can help and  
>> maybe we
>> could find out and enhance the description:
>>
>>
>> I think this one:
>> "r.basins.fill generates a raster map layer depicting subbasins,  
>> based
>> on input raster map layers for the coded stream network (where each
>> channel segment has been "coded" with a unique category value).."
>> is clear.
>> Input is: raster map X from "r.watershed stream=X"
>>
>> Not clear to me is:
>> "...and for the ridges within a given watershed."
>> which is explained as:
>> "The raster map layer depicting ridges should include the ridge which
>> defines the perimeter of the watershed."
>> What should the parameter mean? How should that be stored in a  
>> raster-map?
>> So try out:
>> -> take the stream-network and run r.mapcalc:
>> r.mapcalc "perimeter=if(X,5,null)"
>> Resulting map is a rastermap with value 5, where stream-network is  
>> not
>> null. The five is raster-cells or map units or what else?
>> -> run r.basins.fill with that and see what happens.
>>
>> I guess: from each network-segment the subbasin is created which  
>> has a
>> minimum distance of 5 (cells?) to the stream. So its something like a
>> buffer.
>>
>> ...in contrast to:
>> "...but the map layer of ridges will need to be created by hand (for
>> example, through digitizing done in v.digit)"
>> => the ridges-map here is a vector-file!
>>
>>
>> Achim
>>
>>
>> PS:
>> --%<--
>> DESCRIPTION
>> r.basins.fill generates a raster map layer depicting subbasins,  
>> based on
>> input raster map layers for the coded stream network (where each  
>> channel
>> segment has been "coded" with a unique category value) and for the
>> ridges within a given watershed. The raster map layer depicting  
>> ridges
>> should include the ridge which defines the perimeter of the  
>> watershed.
>> The coded stream network can be generated as part of the r.watershed
>> program, but the map layer of ridges will need to be created by hand
>> (for example, through digitizing done in v.digit).
>>
>> The resulting output raster map layer will code the subbasins with
>> category values matching those of the channel segments passing  
>> through
>> them. A user-supplied number of passes through the data is made in an
>> attempt to fill in these subbasins. If the resulting map layer from  
>> this
>> program appears to have holes within a subbasin, the program should  
>> be
>> rerun with a higher number of passes.
>> --%<--
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>