[GRASS-user] r.stream.extract data range NULL to NULL

[Margherita Di Leo]

Rich,

On Mon, Apr 9, 2012 at 10:33 PM, Rich Shepard <rshepard at appl-ecosys.com>wrote:

>  Running r.stream.extract and removing nulls from the accumulation map
> produces weighted and unweighted stream maps with no data:
>

there would have been a misunderstanding. Probably null values have their
origin in the "weight" map, so IMHO you should run r.null on "weight" map,
and then multiply it for the accumulation map.
In addiction, I also would check the projection, look at the resolution of
your map.. how do you set the resolution? It should  be 30 according to
elevation map. Maybe the resolution of "weight" map doesn't match with the
accumulation (and the elevation) ?

HTH,
madi

>
> r.info dem.noweight.streams
>  Title:     ( dem.noweight.streams )
>   Type of Map:  raster               Number of Categories: 0
>   Data Type:    CELL
>   Rows:         1045
>   Columns:      1457
>   Total Cells:  1522565
>        Projection: Transverse Mercator
>           N: 28660140.36123598    S: 28628801.89941604   Res: 29.98895868
>           E: 549219.21981511    W: 505505.97596796   Res: 30.00222639
>   Range of data:    min = NULL  max = NULL
>   Data Description:
>    generated by r.stream.extract
>
>   Comments:
>    r.stream.extract elevation="dem_proj" accumulation="dem.weighted" th\
>    reshold=1000 d8cut=infinity mexp=0 stream_length=0 stream_rast="dem.\
>    noweight.streams"
>
> and
>
> r.info dem.weighted.streams
>  Title:     ( dem.weighted.streams )
>   Type of Map:  raster               Number of Categories: 0
>   Data Type:    CELL
>   Rows:         1045
>   Columns:      1457
>   Total Cells:  1522565
>        Projection: Transverse Mercator
>          N: 28660140.36123598    S: 28628801.89941604   Res: 98895868
>          E: 549219.21981511    W: 505505.97596796   Res: 30.00222639
>   Range of data:    min = NULL  max = NULL
>   Data Description:
>    generated by r.stream.extract
>   Comments:
>    r.stream.extract elevation="dem_proj" accumulation="dem.weighted" th\
>    reshold=1000 d8cut=infinity mexp=0 stream_length=0 stream_rast="dem.\
>    weighted.streams"
>
>  What might I have done incorrectly now? Again, each step followed the
> r.stream.extract example with the addition of running r.null on the
> accumulation map.
>
> Rich
>
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-- 
Ing. Margherita Di Leo, Ph.D.
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