QGIS - Mandatory "d" values and identifying dead ends, cross points and LFR errors

[Rosie]

Hi, I've recently been working on a project which required input from several data sources to generate a WAsP roughness map, including raster forestry information, project specific vector roughness layers and Corine landcover. I combined forestry heights and downsampled the raster by running filters, converted to vector and after various other data cleaning steps, was able to combine the three information sources.

 For the WAsP polygons to roughness lines tool it wasn't clear from the documentation that even if you're not using displacement height that a "d" column is required within the roughness shapefile layer (with all zero values), in addition to the z0 column. Once I added that the conversion worked. It might be helpful to add a note to the instructions for the polygons to roughness lines tool.

 To check the file I saved as a .map and loaded into WAsP Map Editor (WME), which identified numerous dead ends and cross points as a result of the varied sources of data and operations I'd carried out. A lot of them occurred at points where 3 polygons were connected so I'm not sure if that may be an issue with the polygons to lines converter or just to do with the complexity of all the processing. I fixed them in WME, but wouldn't have been able to identify or fix them as easily in QGIS.  Is there any plan to add a feature to identify cross points, dead ends and LFR errors in the QGIS WAsP toolkit? This would be very helpful for when WME support is withdrawn.

[Rogier]

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For the WAsP polygons to roughness lines tool it wasn't clear from the documentation that even if you're not using displacement height that a "d" column is required within the roughness shapefile layer (with all zero values), in addition to the z0 column. Once I added that the conversion worked. It might be helpful to add a note to the instructions for the polygons to roughness lines tool.

I see, this is a simple bug that I fixed now. The new version will be available soon.

 

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 To check the file I saved as a .map and loaded into WAsP Map Editor (WME), which identified numerous dead ends and cross points as a result of the varied sources of data and operations I'd carried out. A lot of them occurred at points where 3 polygons were connected so I'm not sure if that may be an issue with the polygons to lines converter or just to do with the complexity of all the processing. I fixed them in WME, but wouldn't have been able to identify or fix them as easily in QGIS.  Is there any plan to add a feature to identify cross points, dead ends and LFR errors in the QGIS WAsP toolkit? This would be very helpful for when WME support is withdrawn.

This can be when you use the polygonize script in QGIS or other tools. Those scripts don't insert extra nodes where several polygons meet. You can insert those by searching for the script "Snap geometries to layer" and running that. You can also install windkit and use the script poly2lines:

https://docs.wasp.dk/windkit/io/topo_autogen/windkit.map_conversion.poly2lines.html

[Rosie]

Thanks very much Rogier, I will try those and see if they help.