Monday, July 16, 2012

Detect changes between 2 polygon layers in gvSIG

gvSIG can be used to identify the spatial changes between two polygon vector layers. This can be done by using the Geoprocessing tools' Analysis Overlay difference function. An illustration of this is described below using the scenario of identifying the new vegetation growth and the loss of vegetation cover between a period of time.

Identify new vegetation growth

  1. Start gvSIG OADE. Open a map view. Load and display two polygon layers e.g. vegetation2001.shp and vegetation2011.shp.

  2. Select View | Geoprocessing tools.

    The Geoprocessing tools dialog appears.
  3. Expand the nodes Geoprocessing tools | Analysis | Overlay. Select Difference. Click Open Tool.

    The Analysis tools dialog box appears.
  4. In the Input layer field, choose vegetation2011.
  5. In the Overlay layer field, choose vegetation2001.
  6. In the Output layer field, type in the output file name, e.g. C:\temp\new_growth.shp.
  7. Click OK.

    The polygons representing the new vegetation growth is created.
Identify the loss in vegetation cover
  1. If the Geoprocessing tools dialog is not opened, then select View | Geoprocessing tools.

    The Geoprocessing tools dialog is displayed.
  2. Expand the nodes Geoprocessing tools | Analysis | Overlay. Select Difference.
  3. Click Open tool.

    The Analysis tools dialog box appears.
  4. In the Input layer field, choose vegetation2001.
  5. In the Overlay layer field, choose vegetation2011.
  6. In the Output layer field, type in the output file name e.g. C:\temp\loss_of_vegetation.shp.
  7. Click OK.

    The polygons representing the loss in vegetation cover are created.

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