Fix Proposed WBR Boundary to clear farm boundary artefacts

[seabilwe]

The Proposed WBR boundary has gaps and artefacts that need to be removed (image below), in order to properly use various styles available for a polygon layer.

• [x] Use a simple method to remove the gaps and artefacts from the proposed boundary.

[seabilwe]

Notes

In order to delete the lines and fill in the gaps in the WBR Proposed layer, the procedure outlined below was followed. The procedures were manual.

1. Verify topological errors that exist in the layer

• The Topology checker tool in QGIS was used to check topological errors that exist in the layer.
  • The main error in the layer are gaps

2. Find the difference between the main layer and the extent of the layer

• First extract the extent of the layer using the Extract layer extent tool
• Once the layer is loaded, type in the Processing Toolbox/ Status bar Difference.
• Your input layer will be the extent layer you just generated, and the overlay layer will be the WBR boundary
• Once the layer has been generated, you should get something like this:

3. Use Multipart to Single parts tool

• This generates a new layer in which all geometries contain a single part. Features with multipart geometries are divided in as many different features as parts the geometry contain, and the same attributes are used for each of them.
• This allows us to remove parts of the layer that we need to delete, without deleting the whole layer
• Proceed to delete the external parts of the layer, so that you are left with several polygons covering the gaps of your original layer.
• Results after deletion:

4. Union

• Perform a Union between the original layer and the single parts layer. You can use the SAGA Union tool or the QGIS option, depending on the one that yields the best results. I used the one from SAGA.
• The results from the union should generate this:

5. Cleaning: Removing more artefacts

No process is 100%. From the previous GIF, we can see that there are remaining artefacts such as nodes, lines, and some gaps.

Convert Polygon to Line and vice versa

• You can start by converting the new polygon layer to lines, by using the Polygons to lines tool. Enable editing for the line layer, to remove some lines, that from part of the artefacts we intend to remove.
• Once the line editing is complete, convert the layer back to a polygon, by using the tool Lines to polygons Note that I used SAGA, for most of the georpocessing performed here. The reason for this conversion is to ensure that the lines after conversion are considered as polygons.

Dissolving the layer

• You may see that some artefacts were not completely removed from the layer. Dissolving the layer will be able to remove some remaining artefacts. Using the v.dissolve GRASS tool, it allowed for most of the artefacts to be removed from the layer. Keep in mind to add this in your algorithm:
• The field you want dissolved
• the snap tolerance, which was set to 0
• the minimum area value of your zones, this can be obtained from the attribute table. Note it is also generated from the conversion process performed earlier

The final results looked like this:

Before:

After:

The layer has been uploaded to the wbr db, in the public schema: "wbr_cleaned_boundary_mar2023'

These notes are subject to change

[seabilwe]

Evening @gubuntu, please have a look

Thanks!

[gubuntu]

impressive! if you're happy the zone boundaries themselves are still the same, proceed to use it! Replace the one in the DB so anything using the old layers automatically gets this one...then work on a nice no-fill boundary style that clearly shows the zones

[seabilwe]

@gubuntu I'm getting permission, issues with replacing the 'wbr_boundary_nov22' with 'wbr_boundary_mar23'