Flagging dangles (free end points) with gvSIG

It is quite straightforward to flag dangles (or free end points) using the topology tools in gvSIG. Simply create a new topology rule to check for dangles on a linear layer(s), then run the validation. All the dangles would be flagged out as error points on the map.

To illustrate:

1. Run gvSIG OADE 2010. Load and display a line layer e.g. lines.shp in the Map View.
   
   
   
   Note: the blue rectangles indicate the end points of the line segments for illustration purposes only.
   
2. Select Tools | Topology | Create Topology.
   
   The Create topology wizard appears.
   
   
3. Click Next.
   
   
   
4. In the Topology name field, type in a string e.g. dangles.
   
5. In the Cluster tolerance field, key in a value e.g. 1.
   
6. In the Maximum number of errors, key in a value e.g. 20.
   
7. Under the Layers to include in topology list, toggle on a layer e.g. line.shp. Click Next.
   
   
   
8. Click Add.
   
   The Topology rules dialog box appears.
   
   
9. In the Topology rule drop down list, choose All line geometries of A must be free of dangling nodes. Click OK.
   
   The rule is added to the list.
   
   
10. Click Finish.
    
    A new group named dangles is added to the TOC (legend).
    
    
11. In the legend, click the group dangles.
    
12.  Select Tools | Topology | Validate Topology.
    
    A new layer dangles_error is created under the dangles group. The dangles are flagged in the Map View.
    
    
13. Optional. Click on the dangles_error layer in the legend. Select Layer | Show Attribute Table.
    
    The Table: Attribute table:dangles_error dialog box appears.