More frequently we have a cohabitation of ArcGis
with QGis. We keep ArcGis for heavy operations while
QGis is used for lighter work , even if QGis is quite capable of
assuming much more than that . Free , easier to handle, QGis is more used for portable applications.
But there’s always the
possibility of sharing the data between these two
software
. Towork properly with ArcGis we use geodatabases, but
it
is not possible to access such data from QGis.
Therefore, we choose to export a shapefile that it is easily accessible
by both software . Except that this specific format,
available for more than 30 years does not pose many problems. In
this article, we will discuss, a quite unknown option, the use of
databases SpatiaLite databases, to communicate between both
software
.
If
you want , first of all, to know why it’s worth
using SpatiaLite instead of a shapefile, go directly
to the paragraph Why not a shapefile?
.
And
afterwards, return here.
With QGis, we have already discuss how to work with SpatiaLite databases ( Tutorial databases SpatiaLite under QGis 2.8 Wien ). ArcGis uses may be surprised since the format SpatiaLite is well supported by ArcGis since version 10.2.
What is SpatiaLite?
SpatiaLite is an Open Source Spatial Data
Management Project built above the SQLite
platform.
Here
is an excerpt from the Wikipedia SQLite article:
“
»
SQLite is a relational database management system contained in a C
programming library and SQL language. SQLite
implements in great
part of the SQL-92 standard and ACID properties
.
Unlike traditional database servers, such as MySQL or PostgreSQL, its main feature is to not reproduce the usual client- server schema but to be directly integrated into programs. The entire database (reports, tables, indexes and data) is stored in an independent file of the platform .
D. Richard Hipp , the creator of SQLite, chose to put this library and its source code in the public domain, allowing unrestricted use as well as the open source projects as proprietary projects . The creator as well as part of the SQLite’s main features developers are employed by American Hwaci1society.
SQLite is the most distributed database engine in the world, thanks to its use in many consumer software such as Firefox, Skype, Google Gears, in some products Apple, Adobe and McAfee and in many standard libraries languages like PHP or Python. By its extreme lightness ( less than 300 Kio2), it is also very popular on board systems, including on most modern smartphones: iPhone as well as the mobile operating systems Symbian and Android use it as an embedded database3 . In total, we can count over a billion copies of known and reported to the library « ( see full article )
What to do to be able to use Spatialite?
NOTHING! There is no installation or configuration. You can create and use databases Spatialite from for ArcGIS or QGis, without doing anything special .
How to create a SpatiaLite database with ArcGis
We will use the Python console to create the database SpatiaLite . Open the Python console by clicking on the icon
Firstly we will define the name of the database to create ( argistest.sqlite ) in a variable ( sqlite_database )
Type the command next in the window sqlite_database= ‘C: / qgis /arcgistest.sqlite‘
Then we create the actual database with the following command: a rcpy.gp.CreateSQLiteDatabase(sqlite_database, « SPATIALITY »)
The database is created containing all the necessary tables and views for its management
Warning! The parameter
« SPATIALITY has to be in use
if
you
want
to communicate with QGis or any other software
. The other option, « ST_GEOMETRY » is
specific
to ArcGis and the geometry of the created tables will not be read by QGis or
the others software .
Now
that the base is created you
can
use
it in a standard way , with the catalogue window , to import data
in
the base.
Why not a shapefile?
A demonstration is
better
that
a long speech , here is a small example grouping three reasons not to
use a shapefile as an intermediate format .
Here is a class
of
geodatabase entities. It contains 4 attributes :
Date_and_time_take , type DATE
3
fields of type float r esultat_xxx
The same table after an export in shapefile shows :
Find the difference !
1- The field names are truncated and modified . Here we only have three fields, but when he there are many, there find is complicated . On the other hand, if the shapefile must be recovered after treatment , for example after correction or updated by users, you will have to manually make the correspondence of each field in the shapefile with the fields of the geodatabase.
2- The null values of the attributes digital , indicating it there is no measure , are processed in 0. But 0 is a possible value of measurement . You have no more way of knowing if analysis n / A find no trace of the product or if analysis did not take place. This change is so irreversible .
3- Even if the field is called date and time , you have only the date and you have lost the time . The sql version used by dbf files ( those used in shapefiles) supports only part day- month – year to date. Your hours and minutes are finally passed to the trap, and this is irreversible . The result of the import of the class entity in a SpatiaLite base :
Look again for the difference …
There is none!!
The fields keep their name, values
null are respected
, the date contains well time .
Those
-ci were only three examples of problems but he
there
are others . Why miss this solution?
In QGis there enough Now right click on Spatialite, and connect the base created with ArcGIS.
You can then load the layer in the window cartographic , open the attribute table , etc …
