[GRASS-dev] [GRASS GIS] #2935: r.watershed returns bogus flow direction without warning when using large "virtual" terrain

[GRASS GIS]

#2935: r.watershed returns bogus flow direction without warning when using large
"virtual" terrain
---------------------+-------------------------
 Reporter:  mankoff  |      Owner:  grass-dev@…
     Type:  defect   |     Status:  new
 Priority:  normal   |  Milestone:
Component:  Raster   |    Version:  6.4.4
 Keywords:           |        CPU:  Unspecified
 Platform:  MacOSX   |
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 I'm using the hydropotential, in units Pa, as my "elevation" for
 r.watershed in order to route flow under a glacier. The values are larger
 than a normal elevation, although perhaps not using grass for planetary
 research. The output of "r.info" follows. When I use this with
 {{{r.watershed -a --v elevation=phi accumulation=acch drainage=fdir
 thresh=50 flow=RUh.2k}}}, the {{{fdir}}} results are incorrect.

 If I {{{r.mapcalc 'phi = phi / 1000'  # [Pa] to [kpa]}}}, then things
 work.

 I can provide example files if needed to recreate this.

 {{{
 > r.info phi
 +----------------------------------------------------------------------------+
  | Layer:    phi                            Date: Wed Feb 24 20:37:58 2016
 |
  | Mapset:   PERMANENT                      Login of Creator: mankoff
 |
  | Location: Morlighem_2014
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  | DataBase: /Users/mankoff/data/grass
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  | Title:     ( phi )
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  | Timestamp: none
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 |----------------------------------------------------------------------------|
  |
 |
  |   Type of Map:  raster               Number of Categories: 255
 |
  |   Data Type:    DCELL
 |
  |   Rows:         538
 |
  |   Columns:      301
 |
  |   Total Cells:  161938
 |
  |        Projection: Stereographic
 |
  |            N:    -657600    S:   -3349500   Res: 5003.53159851
 |
  |            E:     864700    W:    -638000   Res: 4992.35880399
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  |   Range of data:    min = -250782  max = 32395007.4
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  |
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  |   Data Description:
 |
  |    generated by r.mapcalc
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  |
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  |   Comments:
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  |    1000 * 9.8 * z_b + 917 * 9.8 * (z_s - z_b)
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  |
 |
 +----------------------------------------------------------------------------+
 }}}

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Ticket URL: <https://trac.osgeo.org/grass/ticket/2935>
GRASS GIS <https://grass.osgeo.org>