[GRASS-user] Different distances to outlet for r.stream.order and r.stream.distance

[Mira Kattwinkel]

Thanks a lot!

I saw that you uploaded a revision. Can you please give me a hint how I 
upgrade to the revised version of r.stream.order? I am running Linux 
Mint 17.3 and Windows 7.

I found that there are nightly pre-built Addon executables for Windows, 
so I will try that tomorrow. What about Linux? Is it sufficient to just 
reinstall the addon?


All the best,

Mira


Am 21.09.2016 um 11:08 schrieb Markus Metz:
> On Tue, Sep 20, 2016 at 10:53 AM, Mira Kattwinkel
> <kattwinkel-mira at uni-landau.de> wrote:
>> Dear List
>>
>> r.stream.order gives, among other output, the distance of current the stream
>> init from the outlet of the catchment ('out_dist'). So for the most
>> downstream segment this is identical to the length of the segment.
>> r.stream.distance calculates the distance to the outlet and results in a
>> raster file. Both are based on a stream raster and a direction raster.
>>
>> When I compare the results, they are slightly different, although based on
>> the same input files (see the attached Fig1). The raster value is 212.33 at
>> the junction, while the out_dist of the line is 237.69. The difference is
>> one cellsize (25.023 in may example), probably due to the horizontal bit of
>> the line at the end (upper right of the figure).
> Yes, this horizontal bit of the line is a bug in r.stream.order, the
> stream vector is leaving the current region or going into a NULL cell.
> All other r.stream.* modules place the outlet on a valid cell. Fixed
> in r69542.
>
>> However, this difference is
>> not fixed. In the middle of the network (Fig2) it is larger (81028.9 -
>> 81002.89 = 27).
> What is the difference in the middle of the network now with r69542?
>
> Markus M
>
>> What is the reason for this difference? Is this a bug or a wanted behaviour?
>>
>> I want to extract the position of points on the network (i.e. upstream of a
>> junction on the lines). To this end, I planned to use the upstream distance
>> of the points and the out_dist of the segments (length(segment) -
>> (out_dist(segment) - upDist(point)) = position(point)).
>> Has anybody another idea how to accomplish this?
>>
>> Thanks a lot,
>> Mira
>>
>>
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-- 
Dr. Mira Kattwinkel
Quantitative Landscape Ecology
Institute for Environmental Sciences
University of Koblenz-Landau
Fortstraße 7
76829 Landau
Germany
Fon: + 49 6341 280-31553