Monday, November 25, 2013

Find dangles using QGIS

QGIS Desktop 2 has a easy to use plug-in - Topology Checker, that can be used to identify dangles in linear features. If it is not installed, then it is a simple matter to use the Plug-in Manager to download and install it, as shown below.

Using the Topology Checker to find dangles is straightforward. Just choose the linear feature layer and define the validation rule(s), and run it. An example usage is illustrated below.

  1. Start QGIS 2. Load and display a linear feature layer e.g. segments.

  2. Select Vector | Topology Checker | Topology Checker.

    The Topology Checker pane appears on the right.

  3. In the Topology Checker pane, click Configure.

    The Topology Rules Settings appear.

  4. In the Current Rules first drop down combo box, choose a linear feature e.g. segments.

    The second and/or third combo boxes are enabled.

  5. In the second combo box, choose a validation rule e.g. must not have dangles. Click Add Rule.

    The rule is added to the list.

  6. Click OK.
  7. In the Topology Checker pane, click Validate All.

    The dangles are listed.

  8. In the list, select one error.

    The dangle is highlighted and centered in the map.

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