There are two things you need to learn: the Python language and how to
use the ArcGis Python geoprocessing library. As for Python, tutorials abound. But
do not forget that you will only need some basics of the language. You will
basically string together already existing ArcGis tools.
Have you decided to get started? It’s time to put all the assets on your
side . It’s already enough complicated to learn a new language, it is useless
to add pitfalls! This is a checklist and a few tips to start smoothly. Firstly
, if you are accustomed to program and Python or another language leaves you
completely indifferent , just take a look at the few traps described below and tackle
down the Python tutorial of your choice .
On the other side, if you back
off, start by convincing yourself that it is not necessary to master Python in
order to use it for our tasks with ArcGis. It is quite possible to link the
processing in a Python script by only knowing the basics of the language .
Warning:The update of the help file does not work for
versions 2.8, 2.8.1 and 2.8.2.A bug causes all changes performed with
the help editor to be lost.Normally, the next update of QGis should
have this problem solved .
You can inform the Model Help by clicking the
Model Help Editor button in the Graphic Modeller window.
This will open the Help Editor window that has three panels. At the top
is an HTML page with placeholders for the description of the algorithm, and
sections for the input and output parameters. At the bottom left you have an
element selection box, and at the bottom right, a text entry box. To edit an
item, select it in the left window and use the box on the right to enter a descriptive
text. Click OK when you are done.
This help information will then be available in the Help tab when
the tool is in run mode.
To run a model from the Graphic Modeller window,
click the Launch Template button :
run a model from the Processing Toolbox panel, first save and close the model.
Then, find the model by accessing Processing |Toolbox |Models , right click on the model to run and select Run
in the context menu.
algorithms are added in the graphic modeller as if they were data input.
Simply select algorithms tab instead of Inputs data,
to observe the corresponding display in the Boxprocessingtool
Once the algorithm to be added is found, double- click, or glide toward the graphic window of the Modeller. To search the algorithm you can do it as you would in the processing toolbox, typing the name in the search box at the top of the algorithm tab.
very widespread false idea according to which the geodatabases
( .gdb ) cannot be read and modified using
within the Esri ArcGIS platform, recent versions of GDAL (and therefore using
applications such GDAL- queQGIS ) are capable
of, effectively, read and extract information from the geodatabases
. The geodatabase file format has become
a very common format for storing and exchanging data space
, in particular since it allows the storage
of multiple data layers and that allows the storage of data layers exceeding
the limits of others specifications .
users, regularly, use geodatabases
when the attribute tables exceed the storage capacity
a shapefile attribute table ( a DBF file is limited to ~ 2 GB
in size ).
This tutorial provides you with the necessary steps
to manage databases in QGIS. Although QGIS can handle several
types of databases, we used SpatiaLite because it provides a lot of features
without the need for a particular installation and very little administration
using the database manager included in QGis, you can perform a certain number
of database operations.
main operations are: indexes creation, spatial and non-spatial views, import
and export data, queries execution. After
discussing the QGis database manager and the SpatiaLite usage guidelines in
this tutorial, you’ll be well equipped to write more complex queries and take
full advantage of the SQL and SpatiaLite SQL commands.
One of the main differences between data management with shapefiles and
a database is the ability to create different “views” for the same
data. In this article, the last in the series devoted to SpatiaLite with QGis,
we’ll discuss how to build SQL queries to generate SpatiaLite views.
DB Manager has a SQL window that allows the construction and execution of SQL
queries on a database. This article shows how to use the SQL window to query a
table and create a SpatiaLite spatial view.
In a previous article we have discussed ( How to create a
SpatiaLite database with QGis 2.8 ) how to import a shapefile
into a SpatiaLite database. The method is the same for other types of spatial
data (kml, gml, …). We will now discuss how to import non-spatialized data
(Excel, txt, csv, …) and especially those containing location attributes (XY,
Lat / Lon, …) while creating their geometries. We will also discuss how to
export SpatiaLite tables as shapefiles.
When we need to use a tool of the QGis toolbox, it is
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
GIS packages was only accessible with the third
party software environment or through a command line
environment. The processing toolbox
third party processing from the QGis interface. The following
suppliers processing are accessible using the toolbox: