[GRASS-user] r.drain problem when flow reach the border

Mon Dec 31 03:16:58 PST 2012

On Sun, Dec 30, 2012 at 11:44 PM, Milton Cezar Ribeiro
<miltinho.astronauta at gmail.com> wrote:
> Hi Markus
>
> I am using this commands.
>
> r.cost -k input=friction_landuse_roads output=cost_map
> start_points=map_source_pt stop_points=map_target_pt --o
> r.drain input=cost_map output=drain_map vector_points=map_target_pt --o

r.drain in GRASS 6.4 does not work with cost surfaces generated with
the Knight's Move (r.cost -k). Actually, r.drain does not work at all
with cost surfaces in GRASS 6.4. You need the direction map together
with the cost surface, and this is only available in 6.5 and 7.

>
> I have not a direction map, and as for other source-target-friction
> maps everything works fine without direction map I thougth that this
> should work for all.

I doubt that it works fine if you do not use the direction map
generated by r.cost, because r.drain modifies the input surface if no
direction map is given, but for a cumulative cost surface these
modifications introduce errors.

>
> If you have the chance, please run the command and take a look that
> the drain line finish on right border.

I see. The output is correct with regard to the input cost surface
only if a direction map is used as indir input for r.drain.

I am going to backport r.cost/r.walk/r.drain from 6.5 to 6.4.

Happy new year,

Markus M

>
> best wishes
>
> miltinho
>
>
> 2012/12/30, Markus Metz <markus.metz.giswork at gmail.com>:
>> On Sun, Dec 30, 2012 at 8:59 PM, Milton Cezar Ribeiro
>> <miltinho.astronauta at gmail.com> wrote:
>>> Hi Rashad
>>>
>>> I tested with the trunk svn, but apparently it still not worked to me.
>>> Are you able to test with my datased?
>>>
>>> https://www.yousendit.com/download/UW16RE9zTkxlM1JBSXNUQw
>>
>> What are the commands you used? I found
>> r.drain input=custo_aux_cost output=custo_aux_cost_drain
>> vector_points=map_target_pt
>>
>> You need to also provide a direction map with the indir option of r.drain.
>>
>> Markus M
>>
>>>
>>> Thanks!
>>>
>>> miltinho
>>>
>>> 2012/12/27, Mohammed Rashad <mohammedrashadkm at gmail.com>:
>>>> Hi Milton,
>>>>
>>>> I think this fix will solve the problem[0]. For elevation data there
>>>> might
>>>> be cases where no path exists ie, only single pixel is the selected path.
>>>> I
>>>> had tested it by myself and it worked.
>>>>
>>>> Please apply the patch and let me know.
>>>>
>>>> If any problem comes in compilation or doing r.drain let me know. It
>>>> will
>>>> be great if you can share the test data you are using in case not
>>>> working
>>>> after applying the patch
>>>>
>>>> [0] http://trac.osgeo.org/grass/attachment/ticket/1840/r.drain.diff
>>>> [1] http://trac.osgeo.org/grass/attachment/ticket/1840/drain.c
>>>>
>>>>
>>>> On Thu, Dec 27, 2012 at 2:31 AM, Milton Cezar Ribeiro <
>>>> miltinho.astronauta at gmail.com> wrote:
>>>>
>>>>> Hi Mohamed and Markus
>>>>>
>>>>> Mohamed, thanks for your reply, I will wait for a solution within GRASS
>>>>> :-)
>>>>>
>>>>> Markus, thanks for your reply,. Sorry  but I disagree a tiny bit,
>>>>> because is expected that between a source and target I will find a
>>>>> solution with the Least Cost path. Do you think that is there any
>>>>> situation where a least cost between source and target will not be
>>>>> found? Maybe if other software provide the soluction, although is not
>>>>> the bestest option, I prefere receive one complete output than a
>>>>> broken one.
>>>>>
>>>>> Happy new year!
>>>>>
>>>>> miltinho
>>>>>
>>>>> 2012/12/23, Markus Metz <markus.metz.giswork at gmail.com>:
>>>>> > On Sun, Dec 23, 2012 at 7:07 PM, Milton Cezar Ribeiro
>>>>> > <miltinho.astronauta at gmail.com> wrote:
>>>>> >> Dear all,
>>>>> >>
>>>>> >> I am running a least cost path analysis combining r.cost and
>>>>> >> r.drain.
>>>>> >> But on some cases, when the least cost path between source and
>>>>> >> target
>>>>> >> reach the border of my map, r.drain stop on that position, and
>>>>> >> target
>>>>> >> point isn´t reached.
>>>>> >
>>>>> > This is correct because at the borders, the direction can not be
>>>>> > determined, the path could lead out of the current region, you can
>>>>> > not
>>>>> > tell.
>>>>> >
>>>>> > Running on other softwares the algorithms the
>>>>> >> source and target is connected using edges without problem.
>>>>> >
>>>>> > If in doubt, I would call it a bug in that other software.
>>>>> >
>>>>> >>
>>>>> >> Any hint are welcome.
>>>>> >
>>>>> > Try to expand the current region
>>>>> >
>>>>> > Markus M
>>>>> >
>>>>>
>>>>>
>>>>> --
>>>>> Miltinho - mcr at rc.unesp.br
>>>>> Laboratório de Ecologia Espacial e Conservação - LEEC
>>>>> Depto de Ecologia - UNESP - Rio Claro
>>>>> Av. 24A, 1515- Bela Vista
>>>>> 13506-900 Rio Claro, SP, Brasil
>>>>>
>>>>> Fone: +55 19 3526-9647 (office)  19 3526-9680 (lab)
>>>>> Cel: 19 9853-3220 / 19 9853-5430
>>>>>
>>>>> Depto Ecologia http://www.rc.unesp.br/ib/ecologia/
>>>>>
>>>>> PG ECO & BIODIV
>>>>> http://www.rc.unesp.br/ib/ecologia/posbiodiversidade/index.php
>>>>>
>>>>> CV
>>>>> http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4792988H6&mostrarNroCitacoesISI=true&mostrarNroCitacoesScopus=true
>>>>>
>>>>> Google citations http://scholar.google.com/citations?user=OWX_2eAAAAAJ
>>>>> _______________________________________________
>>>>> grass-user mailing list
>>>>> grass-user at lists.osgeo.org
>>>>> http://lists.osgeo.org/mailman/listinfo/grass-user
>>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> Regards,
>>>>    Rashad
>>>>
>>>
>>>
>>> --
>>> Miltinho - mcr at rc.unesp.br
>>> Laboratório de Ecologia Espacial e Conservação - LEEC
>>> Depto de Ecologia - UNESP - Rio Claro
>>> Av. 24A, 1515- Bela Vista
>>> 13506-900 Rio Claro, SP, Brasil
>>>
>>> Fone: +55 19 3526-9647 (office)  19 3526-9680 (lab)
>>> Cel: 19 9853-3220 / 19 9853-5430
>>>
>>> Depto Ecologia http://www.rc.unesp.br/ib/ecologia/
>>>
>>> PG ECO & BIODIV
>>> http://www.rc.unesp.br/ib/ecologia/posbiodiversidade/index.php
>>>
>>> CV
>>> http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4792988H6&mostrarNroCitacoesISI=true&mostrarNroCitacoesScopus=true
>>>
>>> Google citations http://scholar.google.com/citations?user=OWX_2eAAAAAJ
>>
>
>
> --
> Miltinho - mcr at rc.unesp.br
> Laboratório de Ecologia Espacial e Conservação - LEEC
> Depto de Ecologia - UNESP - Rio Claro
> Av. 24A, 1515- Bela Vista
> 13506-900 Rio Claro, SP, Brasil
>
> Fone: +55 19 3526-9647 (office)  19 3526-9680 (lab)
> Cel: 19 9853-3220 / 19 9853-5430
>
> Depto Ecologia http://www.rc.unesp.br/ib/ecologia/
>
> PG ECO & BIODIV http://www.rc.unesp.br/ib/ecologia/posbiodiversidade/index.php
>
> CV http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4792988H6&mostrarNroCitacoesISI=true&mostrarNroCitacoesScopus=true
>
> Google citations http://scholar.google.com/citations?user=OWX_2eAAAAAJ