Identifying features with duplicate geometry in QGIS

Question

I am working on a public transport network in one shapefile (polyline type) in QGIS 2.18.

Certain bus routes share the same paths, means that one line-part can repeat more than once. It always has the same identical geometry.

For instance, if I select a feature with 'Identify Features' I will have three outcomes in the Identify results table, see an image below.

I want to select all the features that share the same geometry and further process it. I intend to sign an attribute that says if the layer overlaps.

Can you suggest the most beneficial way?

So far I have tried:

• Vector > Research Tools > Select by location. However, I am not that certain regarding the geometric predicate. Because the 'equals' either 'overlaps' do not give me any sufficient outcome.
• Vector > Geometry Tools > Geometry checker, do not know what to choose in conditions and properties.
• Plugins > Geometry Validator > Validate geometries, does not provide any errors notifications.

Answer 1

Duplicate the layer.

In the processing toolbox use 'Join attributes by location (summary)'.

Use the original and the duplicate layers for the input and join layers.

Select 'equals' as the geometry predicate.

Run.

The attribute table of the resulting layer will have a field in it called "YourIDField_count". Where this is greater than 1 is where you have duplicate geometries.

Now select everything in the joined layer where the count is over 1.

Use these to select by location (geom predicate = equals) from the original layer.

Answer 2

Use the geometry checker plugin to check for duplicates

The Result tab will display a table of duplicate features. You can select features on the map by selecting them in the Result table.

If you choose the option "Fix selected errors, prompt for resolution method" you get a popup like this that allows you to choose to remove duplicates or not.

Answer 3

You can use the Topology Checker Panel and define the rule (your road layer should not have duplicates.)

After defining your rule, you press Ok and you run.

The Tool will give you their Feature ID and if you click to a particular line it will zoom to the layer, for further investigation.

Answer 4

You could modify the Delete duplicate geometries script from QGIS 2.18 where once duplicated features are found which have the exact same geometry, they are stored in a list along with the original feature. You could then select all these features:

layer = iface.activeLayer()
features = layer.getFeatures()
geoms = dict()
for current, f in enumerate(features):
    geoms[f.id()] = QgsGeometry(f.geometry())

cleaned = dict(geoms)
selectedSet = []

for i, g in geoms.iteritems():
    for j in cleaned.keys():
        if g.isGeosEqual(cleaned[j]):
            if i == j or i not in cleaned:
                continue
            if g.isGeosEqual(cleaned[j]):
                selectedSet.extend([g, j])

layer.setSelectedFeatures(selectedSet)