Unit 12 - Script User Interface

Standard input

There is a clear issue related to the script from Unit 11 - PyGRASS scripting. Some modules (r.recode, r.colors) use hardcoded paths to the input files. See code below (rules option).

    Module("r.recode",
           overwrite = True,
           input = "ndvi",
           output = "ndvi_class",
           rules = "/home/user/geodata/models/reclass.txt")

    Module("r.colors",
           map = "ndvi_class",
           rules = "/home/user/geodata/models/colors.txt")

By PyGRASS a content of input file can be defined as a string object and transfered to the command via standard input (stdin_). See a sample code below.

    Module("r.recode",
           overwrite = True,
           input = "ndvi",
           output = "ndvi_class",
           rules = "-",
           stdin_ = "-1:0.1:1\n0.1:0.5:2\n0.5:1:3")

    Module("r.colors",
           map = "ndvi_class",
           rules = "-",
           stdin_ = "1 grey\n2 255 255 0\n3 green")

Note that many of GRASS modules allows sending data via standard input by option value - (dash). In our case the both commands with rules=- option.

Tip

Cleanup routine which removes intermediate data by g.remove can be also defined.

def cleanup():
    Module('g.remove', flags='f', name='region_mask', type='vector')

User interface (UI)

The script lacks user input, all input paramaters are hardcoded. Remember a first modification of the script generated by Graphical Modeler in Unit 11 - PyGRASS scripting.

At first add previously removed lines back to the script.

#%module
#% description: NDVI model version 2
#%end

With these lines included a magic will happen, a standardized GUI dialog appears. Since only module description was defined and no parameters, the dialog offers only global flags like –verbose or –quiet.

Fig. 81 Automatically generated GUI dialog.

Let’s define parameters below:

• region: vector map defining a computation region (required)
• clouds: vector map with cloud mask features (required)
• red: input red channel (required)
• nir: input nir channel (required)
• threshold: threshold for removing small areas (optional)
• output: output vector map (required)

UI definition below.

#%module
#% description: NDVI model version 3
#%end
#%option G_OPT_V_INPUT
#% key: region
#% description: Name of input vector region map 
#%end
#%option G_OPT_V_INPUT
#% key: clouds
#% description: Name of input vector clouds map 
#%end
#%option G_OPT_R_INPUT
#% key: red
#% description: Name of input red channel
#%end
#%option G_OPT_R_INPUT
#% key: nir
#% description: Name of input NIR channel
#%end
#%option
#% key: threshold
#% description: Threshold for removing small areas
#% answer: 1600
#%end
#%option G_OPT_V_OUTPUT
#%end

Fig. 82 GUI dialog with input options.

In the script input parameters are still hardcoded, eg.

    Module("v.overlay",
           overwrite = True,
           ainput = "jena_boundary@PERMANENT",

The input parameters are accesible by options and flags objects which are generated by parse() function.

    options, flags = parser()

Options and flags are dictionaries, where parameters are accessible by option keys, see example below.

    Module("v.overlay",
           overwrite = True,
           ainput = options["region"],

Note

All generated (intermediate) maps can be removed when computation finished.

    Module('g.remove', flags='f', name='region_mask', type='vector')
    Module('g.remove', flags='f', name='ndvi', type='raster')
    Module('g.remove', flags='f', name='ndvi_class', type='raster')
    Module('g.remove', flags='f', name='ndvi_class', type='vector')

Fig. 83 Improved NDVI script in action.

Sample script to download: ndvi-v3.py