When we need to use a tool of the QGis toolbox, it is
usually
in
the heat of the moment and we omit some preliminary
configuration points . As usual,
at one time or another we will have to come back to lift a blockage .
So here are a few
tips to be aware before getting started with the toolbox.
The processing toolbox serves as a portal for accessing
specific processing to QGis but also for third-party
providers . Historically , processing from
other
GIS packages was only accessible with the third
party software environment or through a command line
environment. The processing toolbox
allows
running
directly
third party processing from the QGis interface. The following
suppliers processing are accessible using the toolbox:
• geoalgorithms of QGIS
•
GDAL / OGR
•
GRASS
•
SAGA
•
TauDEM
•
LAStools
•
R
•
Orfeo Toolbox
•
Models
•
Scripts
The last two lines are not third party
packages, but refer to the models you can create
with the QGis graph modeler and PyQGis scripts that you can
create
with the Python Console.
How to format the
processing toolbox
Firstly, we will make sure the processing
toolbox is correctly formatted
to access and
run
the GRASS, SAGA, TauDEM and LAStools algorithms . Most
libraries required are installed
automatically
, but the configuration of these tools
vary
according
to the operating system and to how you have installed
QGIS.
For
example , if you have
used
the
OSGeo installer
you can use the Installation
advanced option to install GRASS 7 otherwise
you
must
manually install GRASS 7 and configure the directories
in
the toolbox.
If
you cannot find a configuration option in the toolbox for a given package, it
means it is not installed .
Refer
to http://docs.qgis.org/2.6/en/docs/user_manual/processing/3rdParty.html for
details installation of different third-party
libraries .
The toolbox formatting includes essentially
the activation or deactivation
of a library , as well as the
definition of the directories used.
To open the formatting window
you must
click
on the menu Treatment->
Options …
To start,
you must ensure that each of the
libraries you plan to use is activated and, according to your
operating system and installation chosen , you will, perhaps, specify the necessary
directories to execute TauDEM , LAStools , and R. The following figure shows that each of the libraries is activated and that the
directories required are thoroughly specified .
Clicking OK updates the display of the toolbox. If you do not use some libraries simply uncheck the Activate box. This simplifies the toolbox.
Overview
of the toolbox
structure
For
the time being, we have not really discussed the interface. We have simply formatted an perhaps, installed the libraries
required to make the function available in the toolbox.
To display the toolbox, you must click on the Process
menu ->Toolbox
The
processing toolbox appears on the right side of the QGIS interface .
However,
by default, most providers algorithms are not visible. You
must click on the option
Simplified interface that is located
the bottom of the toolkit window, scroll through the available options and select so display advanced .
After
selecting the
advanced interface option , finally, you will gain access to the algorithms complete list toolbox:
At
first, you see a list of various libraries
and the number of available algorithms in each of them . When you click the + next of
entries, the list expands to display the subdirectories that bring together
different tools . In addition to browsing manually
through these directories,
there is a search field at the top of the
toolbox. If you are
already familiar with libraries and you look for a specific tool, this can be a more efficient way
to access the algorithms . Even if you are not familiar with the libraries, you can always use the search box
to discover which are the available tools. For
example , if you are
interested in the different ways to visualize or explore the topographic
relationships , you might search by typing ” topograph ” in the text box and discover
that there are ten tools from three different suppliers that relate to the topography .
To launch a processing,
you just have to double click on its name in the toolbox window. The setting window opens
automatically .
The
processing toolbox provides, also, an additional option allowing
access to underlying processing. To that end, you can open an online command window by
clicking on the Process menu ->CommandLine.
It should be noted that
by typing “grid” in the search box , you
get a list of the available algorithms concerning the grids. The main
difference between the two types of research is that when a tool is selected in the drop list of the command line, it opens automatically . Therefore, once you have
a certain degree of
familiarity with the names of the specific tools, the
command line can increase, significantly,
your productivity .
Now that the QGIS processing toolbox is correctly
formatted and that you have
an idea of how it works and its overall organization
, you can start using it and you will save a few blockages !
