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wxGUI Graphical Modeler

DESCRIPTION

       The  Graphical  Modeler is a wxGUI component which allows the user to create, edit, and manage simple and
       complex models using an easy-to-use interface.  When performing analytical operations in GRASS  GIS,  the
       operations  are  not isolated, but part of a chain of operations. Using the Graphical Modeler, a chain of
       processes (i.e. GRASS GIS modules) can be wrapped into one  process  (i.e.  model).  Subsequently  it  is
       easier to execute the model later on even with slightly different inputs or parameters.
       Models  represent  a  programming  technique  used  in  GRASS GIS to concatenate single steps together to
       accomplish a task. It is advantageous when the user see boxes and ovals that are connected by  lines  and
       represent  some  tasks  rather  than  seeing  lines of coded text. The Graphical Modeler can be used as a
       custom tool that automates a process. Created models can simplify or shorten a task which can be run many
       times  and  it  can  also  be  easily shared with others. Important to note is that models cannot perform
       specified tasks that one cannot also manually perform with GRASS GIS.  It  is  recommended  to  first  to
       develop  the  process manually, note down the steps (e.g. by using the Copy button in module dialogs) and
       later replicate them in model.

       The Graphical Modeler allows you to:

           •   define data items (raster, vector, 3D raster maps)

           •   define actions (GRASS commands)

           •   define relations between data and action items

           •   define loops (e.g. map series) and conditions (if-else statements)

           •   define model variables

           •   parameterize GRASS commands

           •   define intermediate data

           •   validate and run model

           •   save model properties to a file (GRASS Model File|*.gxm)

           •   export model to Python script

           •   export model to image file

   Main dialog
       The Graphical Modeler can be launched from the Layer Manager menu File -> Graphical modeler or  from  the
       main toolbar . It’s also available as stand-alone module g.gui.gmodeler.

       The  main  Graphical  Modeler  menu  contains  options  which enable the user to fully control the model.
       Directly under the main menu one can find toolbar with buttons (see  figure  below).  There  are  options
       including  (1)  Create  new  model,  (2) Load model from file, (3) Save current model to file, (4) Export
       model to image, (5) Export model to Python script, (6) Add command (GRASS modul) to model, (7)  Add  data
       to  model, (8) Manually define relation between data and commands, (9) Add loop/series to model, (10) Add
       comment to model, (11) Redraw model canvas, (12) Validate  model,  (13)  Run  model,  (14)  Manage  model
       variables, (15) Model settings, (16) Show manual, (17) Quit Graphical Modeler.

       Figure: Components of Graphical Modeler menu toolbar.

       There  is  also  a  lower  menu  bar  in  the  Graphical modeler dialog where one can manage model items,
       visualize commands, add or manage model variables, define default values  and  descriptions.  The  Python
       editor dialog window allows seeing workflows written in Python code. The rightmost tab of the bottom menu
       is automatically triggered when the model is activated and shows all the steps of running  GRASS  modeler
       modules. In case of errors in the calculation process, it is written at that place.
       Figure: Lower Graphical Modeler menu toolbar.

   Components of models
       The workflow is usually established from four types of diagrams. Input and derived model data are usually
       represented with oval diagrams. This type of model elements stores path to specific data  on  the  user’s
       disk.  It  is  possible  to  insert  vector data, raster data, database tables, etc.  The type of data is
       clearly distinguishable in the model by its color.  Different model elements are  shown  in  the  figures
       below.

           •   (A) raster data:

           •   (B) relation:

           •   (C) GRASS module:

           •   (D) loop:

           •   (E) database table:

           •   (F) 3D raster data:

           •   (G) vector data:

           •   (H) disabled GRASS module:

           •   (I) comment:
       Figure: A model to perform unsupervised classification using MLC (i.maxlik) and SMAP (i.smap).

       Another example:
       Figure:  A model to perform estimation of average annual soil loss caused by sheet and rill erosion using
       The Universal Soil Loss Equation.

       Example as part of landslide prediction process:
       Figure: A model to perform creation of parametric maps used by geologists to predict  landslides  in  the
       area of interest.

EXAMPLE

In this example the zipcodes_wake vector data and the elev_state_500m raster data from the North Carolina
sample dataset (original raster and vector data) are used to calculate average elevation for every zone.
The important part of the process is the Graphical Modeler, namely its possibilities of process
automation.

The workflow shown as a series of commands
In the command console the procedure looks as follows:
# input data import
r.import input=elev_state_500m.tif output=elevation
v.import input=zipcodes_wake.shp output=zipcodes_wake
# computation region settings
g.region vector=zipcodes_wake
# raster statistics (average values), upload to vector map table calculation
v.rast.stats -c map=zipcodes_wake raster=elevation column_prefix=rst method=average
# univariate statistics on selected table column for zipcode map calculation
v.db.univar map=zipcodes_wake column=rst_average
# conversion from vector to raster layer (due to result presentation)
v.to.rast input=zipcodes_wake output=zipcodes_avg use=attr attribute_column=rst_average
# display settings
r.colors -e map=zipcodes_avg color=bgyr
d.mon start=wx0 bgcolor=white
d.barscale style=arrow_ends color=black bgcolor=white fontsize=10
d.rast map=zipcodes_avg bgcolor=white
d.vect map=zipcodes_wake type=boundary color=black
d.northarrow style=1a at=85.0,15.0 color=black fill_color=black width=0 fontsize=10
d.legend raster=zipcodes_avg lines=50 thin=5 labelnum=5 color=black fontsize=10

Defining the workflow in the Graphical Modeler
To start performing above steps as an automatic process with the Graphical Modeler press the icon or
type g.gui.gmodeler. The simplest way of inserting elements is by adding the complete GRASS command to
the Command field in the GRASS command dialog (see figure below). With full text search one can do
faster module hunting. Next, the label and the command can be added. In case that only a module name is
inserted, after pressing the Enter button, the module dialog window is displayed and it is possible to
set all of the usual module options (parameters and flags).

Figure: Dialog for adding GRASS commands to model.

Managing model parameters
All used modules can be parameterized in the model. That causes launching the dialog with input options
for model after the model is run. In this example, input layers (zipcodes_wake vector map and
elev_state_500m raster map) are parameterized. Parameterized elements show their diagram border slightly
thicker than those of unparameterized elements.
Figure: Model parameter settings.

The final model, the list of all model items, and the Python code window with Save and Run option are
shown in the figures below.
Figure: A model to perform average statistics for zipcode zones.

Figure: Items with Python editor window.

For convenience, this model for the Graphical Modeler is also available for download here.

The model is run by clicking the Run button . When all inputs are set, the results can be displayed as
shown in the next Figure:
Figure: Average elevation for ZIP codes using North Carolina sample dataset as an automatic calculation
performed by Graphical Modeler.

Managing model properties
When one wants to run model again with the same data or the same names, it is necessary to use
--overwrite option. It will cause maps with identical names to be overwritten. Instead of setting it for
every module separately it is handy to change the Model Property settings globally. This dialog includes
also metadata settings, where model name, model description and author(s) of the model can be specified.
Figure: Model properties.

Defining variables
Another useful trick is the possibility to set variables. Their content can be used as a substitute for
other items. Value of variables can be values such as raster or vector data, integer, float, string value
or they may constitute some region, mapset, file or direction data type. Then it is not necessary to set
any parameters for input data. The dialog with variable settings is automatically displayed after model
is run. So, instead of model parameters (e.g. r.import a v.import, see the Figure Run model dialog above)
there are Variables.
Figure: Model with variable inputs.

The key point is the usage of % before the substituting variable and settings in Variables dialog. For
example, in case of a model variable raster that points to an input file path and which value is required
to be used as one of inputs for a particular model, it should be specified in the Variables dialog with
its respective name (raster), data type, default value and description. Then it should be set in the
module dialog as input called %raster.
Figure: Example of raster file variable settings.
Figure: Example of raster file variable usage.

Saving the model file
Finally, the model settings can be stored as a GRASS GIS Model file with *.gxm extension. The advantage
is that it can be shared as a reusable workflow that may be run also by other users with different data.

For example, this model can later be used to calculate the average precipitation for every administrative
region in Slovakia using the precip raster data from Slovakia precipitation dataset and administration
boundaries of Slovakia from Slovak Geoportal (only with a few clicks).

Handling intermediate data
There can be some data in a model that did not exist before the process and that it is not worth it to
maintain after the process executes. They can be described as being Intermediate by single clicking using
the right mouse button, see figure below. All such data should be deleted following model completion. The
boundary of intermediate component is dotted line.
Figure: Usage and definition of intermediate data in model.

Using the Python editor
By using the Python editor in the Graphical Modeler one can add Python code and then run it with Run
button or just save it as a Python script *.py. The result is shown in the Figure below:
Figure: Python editor in the wxGUI Graphical Modeler.

Defining loops
In the example below the MODIS MOD13Q1 (NDVI) satellite data products are used in a loop. The original
data are stored as coded integer values that need to be multiplied by the value 0.0001 to represent real
ndvi values. Moreover, GRASS GIS provides a predefined color table called ndvi to represent ndvi data.
In this case it is not necessary to work with every image separately.
The Graphical Modeler is an appropriate tool to process data in an effective way using loop and variables
(%map for a particular MODIS image in mapset and %ndvi for original data name suffix). After the loop
component is added to model, it is necessary to define series of maps with required settings of map type,
mapset, etc.
Figure: MODIS data representation in GRASS GIS after Graphical Modeler usage.

When the model is supplemented by all of modules, these modules should be ticked in the boxes of loop
dialog. The final model and its results are shown below.
Figure: Model with loop.

Figure: MODIS data representation in GRASS GIS after Graphical Modeler usage.

The steps to enter in the command console of the Graphical Modeler would be as follows:
# note that the white space usage differs from the standard command line usage
# rename original image with preselected suffix
g.rename raster = %map,%map.%ndvi
# convert integer values
r.mapcalc expression = %map = %map.%ndvi * 0.0001
# set color table appropriate for nvdi data
r.colors = map = %map color = ndvi

AUTHORS

       Martin Landa, OSGeoREL, Czech Technical University in Prague, Czech Republic
       Various manual improvements by Ludmila Furkevicova, Slovak University of Technology in Bratislava, Slovak
       Republic

SOURCE CODE

       Available at: wxGUI Graphical Modeler source code (history)

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual

wxGUI Graphical Modeler

DESCRIPTION

EXAMPLE

SEE ALSO

AUTHORS

SOURCE CODE