Unable To Clean Incorrect Geometries with Grass?

Question

Software:

QGIS 2.18.10

GRASS GIS 7.2.1

GitHub Repository Link: Police

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Having difficulty fixing incorrect geometries for nypolicew84.zip shapefile (check GitHub link)

Errors when using GRASS to fix issue. Is there anything I am missing? Or is there a more straight-forward way to fix shapefile. Please assist.

QGIS file also in GitHub

Below are the steps:

1. Open Topology Checker

2. Click on Configuration

3. Select must not have invalid geometries

4. Rule gets added

5. Click on Validate All

6. Error Found

7. Zoom in to see all errors

8. Open GRASS GIS and set location

9. Follow prompts to set location. Kept at default

10. Keep EPSG

11. Select EPSG 4326

12. Get Unlabeled Error

13. Finish is grayed out

Answer 1

I had a look at your project and found a couple of polygon errors, using Check Validity tool (in Processing, under QGIS Geoalgorithms). That gives more detailed error messages than topology checker plugin . It also splits your layer into valid and invalid geometries.

The Topology Checker plugin checks a lot of things, but doesn't appear to give a more detailed reason WHY a geometry is invalid.

Looking at the "Invalid output" layer, two of the precincts have the following errors:-

Ring 0 has less than 4 points

You might want to try running v.clean (from Processing, rather than the GRASS GUI). I tend to use processing when I can, as it handles a lot of the setup (projections, regions) for you.

After running v.clean with default settings, then running topology checker on the output, the geometries show up as clean.

Edit

After running this fix the Duplicate ... errors by going to Vector - Geometry tools - Singleparts to multipart