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

[Markus Metz]

On Mon, Jun 27, 2011 at 8:03 AM, Johannes Radinger <jradinger at gmx.at> wrote:
>
> Am 27.06.2011 um 02:56 schrieb jentjr:
>
>> All,
>>
>> I am trying to use r.stream.extract with the National Hydrography Dataset
>> Plus, which includes elevation, flow direction and flow accumulation maps. I
>> recently read the paper by Jasiewicz and Metz that states, "...network
>> modeling is based on accumulation maps that are created internally or
>> created with an external GIS software or as the result of map algebra."
>> However, I get the following when I try to use the module with the NHDPlus
>> data:
>>
>> ERROR: Accumulation map does not match elevation map!
>
> I think you have to have all the input maps with the same spatial extend and the
> same grid resolution to be able to process it with r.stream.*
> Did you check for that?
>
Matching extents are not required, but if the accumulation map has
been computed for only a part of the elevation map, the current region
must be set to the accumulation map, not the elevation map. Then it
should work. Alternatively, create a MASK with value NULL where the
accumulation map is NULL, otherwise 1 (or anything but NULL or zero).
The resolution of the elevation map and the accumulation map should
always match.

Markus M