We have already discussed the geometry validation in a series of articles. Particularly, you can read the article The geometry validation tools (5) with QGis for the validation tools with QGis 2.8
Version 2.12 brings a new plugin that changes the game. Here is a list of those main characteristics .
Firstly, let’s see what does not change: there is no documentation regarding the tools used by the plugin. It is true that in order to develop those tools implies a very hard job, but using a tool without knowing what is actually done is not very reassuring .
We are going to proceed as for the aforementioned series of articles, by taking a vector layer with errors and following the behaviour of the plugin. We will be using the same working layer .
” We will use a layer of Italian communes provided by ISTAT, the Italian Statistical Institute. This is the layer used in the geometry validation page of Spatialite: SQL functions based on liblwgeom support version 4.0.0 .
The layer is downloadable in this link: . ”
The QGis version used is 2.12.0
Activation of the plugin
The plugin is installed by default with version 2.12 but not activated . You must activate it :
Extension -> Install / Manage Extensions then check the box in front of Check geometry
Launching the plugin Load the data layer you want to check and then click the Vector menu ->GeometryTools->Checkgeometries
The plugin settings window displays.
As you can see, the window includes several blocks of parameters . These blocks correspond to the different types of geometry error supported by the plugin. Here is a graphic synthesis :
The first one includes the basic elements of geometries validation: the auto-intersections, the duplicated nodes and the polygons with less than three nodes (not shown in the previous image).
In the second block you must choose the type of geometry to validate (point, line , polygon , … ).
The third block corresponds to the management of the holes and archipelagos. You authorize the polygons with holes or not, according to your knowledge of the data , and you authorize archipelagos polygons or not.
The fourth block used to validate data according to minimal parameters of segment length, angle, area and width. It becomes obvious that a deeper knowledge of the data is essential to configure these parameters .
The last block allows topological validation , by looking for duplicates, entities within other entities , partial entities overlays and interstices between entities .
Plugin test Firstly, let’s test a simple configuration, only taking in account the geometry validity (first block of parameters ), to compare the result with the tools of previous QGis versions.
The number of detected errors is 476. This figure must be compared to those obtained in previous tests :
Display items Search :
| Software | Nb errors found | |
| ArcGis 10.3.1 | 0 | |
| SpatiaLite | 19 | |
| postgis | 19 | |
| FME 2015 | 19 | |
| Geomedia | 28 | |
| Qgis 2.8 | Verify topol . | 19 |
| Valid. Geom . | 129 |
Viewing items 1 to 7 of 7 items
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Being 4 times larger than those observed with the geometry validation tool available in QGis 2.8 it would be interesting to see what are these new errors detected .
Nevertheless, the only available indication is the name of the error : Type of geometry
( multipolygon ) and the coordinates of the centroid of the polygon concerned .
Despite the efforts deployed, it was impossible to see the errors in most communes indicated as error .
Therefore, we have tried the automatic correction options of the plugin but despite the installation on several positions with different systems and configurations, we have got a QGis crash with every attempt of correction.
Conclusions
The plugin appears be more effective in the detection of geometry errors , but it presents, in its current stage of development two major problems:
- a lack of accurate location of the error for the concerned geometry concerned
- a regular crash of the automatic correction module .
To follow with interest, as it looks very promising .
