- Start SAGA GIS. Load and display the cities and the state boundary polygon in a map view.
- Select Modules | Shapes | Points | Thiessen Polygons.
The Thiessen Polygons dialog box appears.
- In the input Points field, choose the point layer, e.g. 01. cities_in_texas.
- In the output Polygons field, select create. Click Okay.
The Thiessen polygons layer (02. cities_in_texas [Thiessen Polygons] is created. The polygons are spread out over some arbitrary four points.
- Select Modules | Shapes | Polygons | Polygon Clipping.
The Polygon Clipping dialog box appears.
- In the Clip Features field, select the State boundary polygon layer, e.g. 01. texas.
- Select the Input Features field and click the [...] button.
The Input Features dialog box appears.
- In the left list, select the Thiessen Polygons layer, e.g. 02. cities_in_texas [Thiessen Polygons]. Click the > button. Click Okay.
The Input Features dialog box is closed.
- Click the Okay button.
The Thiessen polygons are nicely clipped to the State polygon.
Monday, July 29, 2013
Use Saga GIS to create Voronoi or Thiessen polygons
The new version of Saga GIS 2.1 has a functional Thiessen polygon command. Previously, a bug in the function creates erroneous polygons. Here is an example of using the command to create Voronoi or Thiessen polygons from discrete points with some polygon clipping thrown in for aesthetic effects. The example shows how to create polygons of cities in the great State of Texas.