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

[johnboyd at netspace.net.au]

Thanks Nicolas,

 

I was careful to use the correct CRS.  Luis Eduardo suggested I save in the SAGA format, when I do I have no issues, the file seems to become corrupted when the temporary filled layer is resampled to .tiff.

Regards

John

 

 

From: Nicolas Cadieux <njacadieux.gitlab at gmail.com> 
Sent: Saturday, 21 August 2021 1:03 AM
To: johnboyd at netspace.net.au
Cc: qgis-user at lists.osgeo.org
Subject: Re: [Qgis-user] Issue extracting Strahler order from QGIS saved DEM

 

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





Le 20 août 2021 à 06:44, johnboyd at netspace.net.au <mailto: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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