Tutorial: Automate Stream & Catchment Delineation using the Graphical Modeler

3. Create the graphical model for stream delineation

3.2. Reproject and clip DEM

The next step to implement in our graphical model is to reproject the DEM mosaic to UTM Zone 32N/WGS-84 and to clip the DEM to the bounding box. This can be done with one tool.

We first need to add the bounding box polygon as an input vector layer.

1. Switch back to the Input panel and double click on Vector Layer.

2. Type Bounding box at Description and choose Polygon as Geometry Type. Keep the Mandatory box checked.

In this way the user needs to provide a bounding box polygon vector layer.

3. Click OK.

4. Now switch to the Algorithms tab and search for the Warp (reproject) algorithm and double click.

5. In the Warp (reproject) dialogue replace the Description with Reproject and clip DEM.

6. At Input layer click the button and choose Algorithm Output.

Because we have only one other algorithm this will be automatically the output from the Mosaic DEM Tiles process.

The Source CRS is known, so keep it blank. We need to change the Target CRS to the one from the provided bounding box layer.

7. At Target CRS click the button and choose Model Input.

It will automatically select the Bounding box layer.

8. Keep the Resampling method to use at Nearest Neighbour so the original pixel values are preserved as much as possible. Set the Nodata value for output bands to -9999. Set the Output file resolution to 30 meters.

The dialogue should now look like this:

We still need to clip to the extent of the bounding box.

9. Click the Show advanced parameters button.

10. Choose here for the Georeferenced extents of the output file to be created the Model input Bounding box layer.

11. Click OK.

Now your screen should look like the figure below.

We can proceed by adding the next step.