[GRASS-dev] Re: [GRASS GIS] #518: negative flow accumulation with r.watershed SFD or MFD

GRASS GIS trac at osgeo.org
Fri Mar 6 03:18:38 EST 2009

#518: negative flow accumulation with r.watershed SFD or MFD
  Reporter:  dylan        |       Owner:  grass-dev at lists.osgeo.org
      Type:  enhancement  |      Status:  new                      
  Priority:  major        |   Milestone:                           
 Component:  default      |     Version:  svn-develbranch6         
Resolution:               |    Keywords:  r.watershed              
  Platform:  Linux        |         Cpu:  x86-32                   
Comment (by mmetz):

 IMHO, there is still some cleaning up to do for r.watershed. I left some
 things in it for backwards compatibility. One such thing is the "visual"
 output which I regard as obsolete because "accumulation" output now comes
 with a (better I hope) colortable by default.
 The "visual" output could be removed and another output option be added,
 e.g. called "absacc" that gives absolute accumulation values. That would
 however break backwards compatibility, a new flag would not.

 There is a good reason *not* to add this option/flag, nicely illustrated
 by Dylan creating this ticket. The purpose of negative accumulation values
 is to make people wonder what on earth is going here, then figure out that
 not the whole catchment area under study was included and expand the
 computational region accordingly to get proper results: only positive
 accumulation values for the catchment under study.

Ticket URL: <http://trac.osgeo.org/grass/ticket/518#comment:3>
GRASS GIS <http://grass.osgeo.org>

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