#2935: r.watershed returns bogus flow direction without warning when using large
"virtual" terrain
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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 )
|
| Timestamp: none
|
|----------------------------------------------------------------------------|
|
|
| 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
|
| Range of data: min = -250782 max = 32395007.4
|
|
|
| Data Description:
|
| generated by r.mapcalc
|
|
|
| Comments:
|
| 1000 * 9.8 * z_b + 917 * 9.8 * (z_s - z_b)
|
|
|
+----------------------------------------------------------------------------+
}}}
Now that grass supports other planets https://grasswiki.osgeo.org/wiki/Planetary_mapping it is likely others
will run into similar issues when flow routing over terrain with values
significantly larger than Earth topography.
Now that grass supports other planets https://grasswiki.osgeo.org/wiki/Planetary_mapping it is likely others
will run into similar issues when flow routing over terrain with values
significantly larger than Earth topography.