# Unit 08 - Modeler¶

Graphic Modeler allows creating, editing, and managing complex models in easy-to-use graphical user interface. Using Graphical Modeler, that chain of processes (ie. GRASS modules) can be wrapped into one process (model). The model can be executed repeatedly with slightly different inputs or parameters.

Our first model will be simple as much as possible based on Unit 05 - Perform computation. Actually the model will perform two operations:

2. compute NDVI (i.vi)

Graphical Modeler can be launched from menu File ‣ Graphical modeler or by Graphical Modeler from main toolbar (or alternatively as g.gui.gmodeler module from console).

Fig. 58 Graphical Modeler.

GRASS modules can be added to the model from menu Model ‣ Add command or by Add command (GRASS module) to the model from main toolbar.

Fig. 59 Add commands (GRASS modules) to the model, in this case r.mask.

After adding r.mask module to the model let’s open its properties dialog by double-click and enter vector map to be used as a mask. Don’t forget to enable inverse mask by -i flag.

Fig. 60 Define parameters for r.mask, a vector map used for creating a mask.

In similar way will be added to the model second command i.vi (properties dialog for this command is open automatically because there are required options which must be set).

Fig. 61 NDVI model version 1.

It’s good idea to set metadata for the model and enable overwriting data produced by model (Model ‣ Model properties).

Fig. 62 Define model properties and enable overwriting data produced by model.

Let’s try out our first model. You can run the model repeatedly on different computation regions. You can quickly change current computation region by Set computation region extent interactively from Various zoom options in Map Display.

Fig. 63 Change computation region before running the model.

Important

Before changing the region it’s good idea to remove mask if exists.

r.mask -r


Now let’s run our model by Run model. Progress is printed into Command output.

Fig. 64 Model computation progress.

After redrawing map display Render map (assuming that we have already displayed raster map of NDVI in map display), we should see a difference.

Fig. 65 New NDVI raster map computed by the model.