[GRASS-user] Re: r.stream.extract with external flow accumulation maps

[Jarek Jasiewicz]

On 06/27/2011 05:12 PM, Mark Seibel wrote:
>> I believe that the flow accumulation grid was produced using ArcHydro. I put
>> the link to the data set that I am using below if anyone wants to try it
>> out.
> Hi.  Not sure if this is the issue, but I recall this from the manual.
>
> "
> accumulation
> Input map, optional: Accumulation values of the provided accumulation
> map are used and not calculated from the input elevation map. If
> accumulation is given, elevation must be exactly the same map used to
> calculate accumulation. If accumulation was calculated with
> r.terraflow, the filled elevation output of r.terraflow must be used.
> Further on, the current region's resolution should be identical to the
> accumulation map. Flow direction is first calculated from elevation
> and then adjusted to accumulation. It is not necessary to provide
> accumulation as the number of cells, it can also be (adjusted) total
> contributing area in square meters or any other unit.
> "
>
> Mark

This error message appears when there are nulls in accum map in the 
interest area. Try to change nulls to different values let say 0 and 
tell what happened.
J.
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