How do I topologically clean "pointy bridges" using GRASS v.clean?

Question

I have a shapefile with hundreds of pointy areas connected at the tip, forming a "pointy bridge". This creates a self-intersection and duplicate node. I'm not exactly sure what this type of error is called, so I do not know which v.clean parameters to use. How do I fix this using v.clean? I do not care about splitting the bridge vs. merging the bridge - just want to get rid of the error.

The last thing I tried was running v.clean with these parameters, and it did nothing:

break:0 bpol:0 rmdupl:0 rmbridge:0 rmdac:0

Answer 1

I would proceed as follows:

1. Creating a small test study to work on. It should contain those overlapping vertex points.

2. Apply the v.clean algorithm, fine-tuning the break parameter.

3. Once happy with the threshold value, run it on the whole dataset.

Hope this helps!

Answer 2

According to v.clean help, section rmbridge

A bridge is an area type connection of an island (polygon in a polygon) to the outer polygon. This is topologically incorrect (but OGC Simple Features allow it).

This is what you have here, as rings inside your polygons are connected together.

Therefore, as @Elio Diaz suggested, the best solution would be to go with a buffer, though I'd go with a small positive value (0.01 m or less, depending on your dataset), in order to separate the different rings without making a notable difference on the dataset.

Then you should have no more errors in your layer, or be able to clean them easily.

The problem you have in your dataset is that the points have to be identical to represent your rings, but this is not allowed by topology. Using the buffer method and separating the rings, even with a hair, is enough to correct this behaviour.