[Qgis-user] Issue extracting Strahler order from QGIS saved DEM

[Nicolas Cadieux]

"Nicolas the problem with saving the raster using QGIS processes is the 
resampling when converting sgrd to tif"

That was my conclusion also but//I was trying to figure out if this was 
a bug or not.  If you use the temporary file created as is, it works well.

Thanks!

Nicolas


On 2021-08-20 11:23 a.m., Luis Eduardo wrote:
> Very true John, that's another detail, some algorithms need a 
> cartographic projection to work, for example upslope area.
>
> Nicolas the problem with saving the raster using QGIS processes is the 
> resampling when converting sgrd to tif, if you perform the same 
> process as temporary it does not fail.
>
>
> On Friday, August 20, 2021, 11:02:40 AM GMT-4, Nicolas Cadieux 
> <njacadieux.gitlab at gmail.com> wrote:
>
>
> Hi,
> When you save the file, are you changing the crs?  If the ordinal DEM 
> is in meters and the exported file in long last, the algorithm could 
> go funny on you as some algorithms need files that are in meters to 
> work well.
>
> Btw, would you be using saga in processing to do this?  Is so.  I have 
> had a problem in the past where I could use a tiff, fill the sinks and 
> then extract streams all in one shot. But if I saved the fill sink 
> file and tried to use it later, I would get unusual results in th 
> stream.  If you have this problem, we should file a bug report.
>
> Nicolas Cadieux
> https://gitlab.com/njacadieux <https://gitlab.com/njacadieux>
>
>> Le 20 août 2021 à 06:44, johnboyd at netspace.net.au a écrit :
>>
>> 
>
> Hi All, I am relatively new to GIS and was hoping for some help with a 
> problem I have.
>
> When I load a DEM (tiff) file from an external source and fill sinks I 
> can extract the Strahler order without issue. However after I save the 
> file using the QGIS export feature and attempt to extract the Strahler 
> order there is an issue where I appear to just get many short streams 
> that don’t connect. Looking at the layer attributes between the 
> unsaved file and the saved one they appear identical.
>
> I would appreciate some suggestions as it is frustrating not being 
> able to save the updated DEM so it works.
>
> Regards
>
> John
>
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-- 
Nicolas Cadieux
https://gitlab.com/njacadieux

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