This plugin helps to change the datasources of many layers at once, for example to create different versions of the same project on different extents.

You can use some variables such as {$myvar} inside the layer datasource template, and then define theses variables (from a table or from an input vector source).

Finally you apply the variables values on every configured layer via the apply button, and you can see the changes before saving the project.

You can install the plugin from QGIS extension manager. At present, it has the status "experimental".

At first, you must set up a QGIS project with some layers. This project will serve as a basis to create derived child projects. Once you have a project, you can open the plugin main dialog : Menu Extension / Dynamic Layers

The project layers are listed in the table, which the following properties

• id : Internal QGIS layer id ( stored in project *.qgs file )
• name : The layer name ( as defined in QGIS legend )
• dynamicDatasourceActive : True means the layer is activated : the dynamic datasource content set in the bottom text box will be used when applying variables on the project.

The activated layers have a green background. You can sort the layers in the table by clicking on one of the header columns.

This interface allows you to activate dynamic datasource for the selected layers ( the layer highlighted in the table above ).

You can copy the current datasource from the layer definition by clicking on the Copy from current datasource button.

Then you can change the datasource, and use variables, with the syntax {$varname} by changing "varname" by any name you want ( but you need to use only letters and digits, no spaces or punctuation chars ).

For example, if the original layer datasource for a Shapefile is

/tmp/town_france.shp

You can use a "country" variable

/tmp/town_{$country}.shp

You can use as many variables as needed, and for any type of datasource. For example, you could change a username or table definition of a PostGIS layer, or a WHERE clause, like this

service='myservice' sslmode=disable key='gid' table="(
SELECT row_number() OVER () AS gid, *
FROM mytable
WHERE year = {$year}
)" sql=

We have seen above that you can use variables to define a new layer datasource.

You can also use variables

• inside the layers **title and abstract ** : Open the vector layer properties dialog, and in the Metadata panel, you can use variables in the definition of the title and the abstract properties
• in the vector layers field aliases: in the vector properties dialog, tab Fields, you can use variables inside the aliases defined for each field.

When applying variables with the plugin, all these properties will also be updated. (See the "Set variables" chapter further on)

This tab allows you to define 2 differents things:

• Some project OWS Server properties, used only if you publish your project with QGIS Server: Project title (The title of the map ) and Project description ( the map description ). You can also use variables in these parameters, such as the following example for the title

Map of the towns of {$country} (year : {$year} )

You can use the button Copy properties from project to get the title and description wich are set in the project properties tab of QGIS ( Menu Project / Project properties )

• An extent layer and extent margin. When applying the variables on the project, the plugin will zoom to the extent of the selected layer, plus the given margin.

You can add or remove variables in the table by using the form at the bottom. You can also modify the variable value by entering a new value in corresponding the table cell.

Once you have added your variables and added a value for each one, you can apply variables on project by clicking on the correspondong button.

This will replace each activated layer datasource by the dynamic datasource modified via the variables, and then zoom to the extent layer.

You can now save the project as another project, or simply save the current project. All the configuration is stored in the QGIS project, so you can reuse it in the future.

You can use a project vector layer as an input for variables. In this case, each chosen layer field will be used as variable name.

You must then use a QGIS expression to filter one line of the source layer (if more than one line is returned by the expression filter, the first feature will be used ).

For example, if your source layer has this attribute table

And if you use the expresion

id = 3

You will have the following variables and values

Once source layer and expression are set, you can apply the found variables on your project by clicking on the button Apply on project

This tab will show the plugin log messages.

Video tutorials:

• plugin presentation : https://vimeo.com/141541813
• use a vector layer as a variable data source : https://vimeo.com/141546964

We assume that you are working on a fresh install with Apache and FCGI module installed with:

$ sudo apt-get install apache2 libapache2-mod-fcgid
$ # Enable FCGI daemon apache module
$ sudo a2enmod fcgid

See : http://qgis.org/fr/site/forusers/download.html

To install QGIS Server, after having added the official QGIS package repository and added the public key, you can just do

$ sudo apt-get install qgis-server python-qgis

$ sudo mkdir -p /opt/qgis-server/plugins
$ cd /opt/qgis-server/plugins
$ sudo wget https://github.com/3liz/QgisDynamicLayersPlugin/archive/master.zip
$ # In case unzip was not installed before:
$ sudo apt-get install unzip
$ sudo unzip master.zip
$ sudo rm master.zip 
$ sudo mv QgisDynamicLayersPlugin-master DynamicLayers

You can create a dedicated Apache virtual host for QGIS Server, or modify an existing host by adding some environment variables.

Here is an example of a dedicated virtual host configuration The virtual host configuration, stored in /etc/apache2/sites-available/001-qgis-server.conf:

    <VirtualHost *:80>
        ServerAdmin webmaster@localhost
        DocumentRoot /var/www/html

        ErrorLog ${APACHE_LOG_DIR}/qgis-server-error.log
        CustomLog ${APACHE_LOG_DIR}/qgis-server-access.log combined

        # Longer timeout for WPS... default = 40
        FcgidIOTimeout 120
        FcgidInitialEnv LC_ALL "en_US.UTF-8"
        FcgidInitialEnv PYTHONIOENCODING UTF-8
        FcgidInitialEnv LANG "en_US.UTF-8"
        FcgidInitialEnv QGIS_DEBUG 1
        FcgidInitialEnv QGIS_SERVER_LOG_FILE /tmp/qgis-000.log
        FcgidInitialEnv QGIS_SERVER_LOG_LEVEL 0
        FcgidInitialEnv QGIS_PLUGINPATH "/opt/qgis-server/plugins"

        # ABP: needed for QGIS HelloServer plugin HTTP BASIC auth
        <IfModule mod_fcgid.c>
            RewriteEngine on
            RewriteCond %{HTTP:Authorization} .
            RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
        </IfModule>

        ScriptAlias /cgi-bin/ /usr/lib/cgi-bin/
        <Directory "/usr/lib/cgi-bin">
            AllowOverride All
            Options +ExecCGI -MultiViews +FollowSymLinks
            Require all granted
            #Allow from all
      </Directory>
    </VirtualHost>

Enable the virtual host and restart Apache:

$ sudo a2ensite 001-qgis-server
$ sudo service apache2 restart

You need to give write permission to the apache user (for example www-data ) in order to enable the server plugin to write a new project in it. Make sure the folder has got the right permissions.

Now you must be able to use the plugin server side !

This plugin contains a filter for QGIS Server, which allows to create a child project based on a "parent" project configured with Dynamic layers. Once instaled on server, you can use a new request with the following parameters

• SERVICE : dynamiclayers (must be spelled corectly )
• MAP : the full path to the parent project. For example "/tmp/someproject.qgs"
• DLSOURCELAYER : the name of the source layer defined in the Set variables from a vector layer. For example "variable_source"
• DLEXPRESSION : a QGIS expression to select the feature from the source layer wich contains the needed data for the child project to be generated. For example : "id = 3"

Of course, the expression must be url-encoded. Here is an request URL example

http://localhost/cgi-bin/qgis_mapserv.fcgi?MAP=/tmp/someproject.qgs&SERVICE=dynamiclayers&DLSOURCELAYER=variable_source&DLEXPRESSION=%22id%22%3D3

This request will ask the DynamicLayers Server plugin to create a child project based on the source project "variable_source" ( configured via the desktop QGIS plugin ), and will send back a JSON response containing the name of the created project.

For example:

{
        "status": 1,
        "childProject": "someproject__variable_source_idIN3.qgs",
        "message": "Child project has been updated"
}

If the child project has already been created before, the plugin will not recreate it, but return the following response

{
        "status": 1,
        "childProject": "someproject__variable_source_idIN3.qgs",
        "message": "Child project is already up-to-date"
}

But if you have modified the parent project in the meantime, the plugin will detect that the parent project has been changed, and will recreate the child project.

Lizmap Web Client V3 (currently the master branch ) has the capabilities to use a parent project and to generate a new map based on the plugin DynamicLayers.

Of course, the QGIS plugin DynamicLayers must been installed, as described above.

You must then install the Lizmap module dynamicLayers. This module is shiped with Lizmap Web Client 3 and above, but is not installed by default.

To do so, you must add the following line in the section [modules] of lizmap local configuration file. In the following example, we assume that Lizmap Web Client is already installed and working, and the root of Lizmap installation is /var/www/lizmap-web-client/

cd /var/www/lizmap-web-client/
nano lizmap/var/config/localconfig.ini.php

In this file, you should see a section [modules], if not create it, and activate the module dynamicLayers by writing its access level as follow:

[modules]

dynamicLayers.access = 2

Then save the file. Now you can install the module via

sudo lizmap/install/set_rights.sh www-data www-data
php lizmap/install/installer.php

If you have a Lizmap map corresponding to this URL

http://lizmap.localhost/index.php/view/map/?repository=somerepo&project=someproject

You can for example configure the QGIS project someproject.qgs with the plugin Dynamic Layers, and then pass some parameters in a dedicated URL to let the combo Lizmap / DynamicLayers create a derivated map based on the initial map. For example, use the following URL:

http://lizmap.localhost/index.php/dynamicLayers/map/?repository=somerepo&project=someproject&dlsourcelayer=variable_source&dlexpression=%22id%22%3D3

Basically, this URL is the same as the normal Lizmap one, but:

• we have replaced view/map/ by dynamicLayers/map/
• we have added the 2 parameters dlsourcelayer and dlexpression (in lower case) containing the same values as shown previously.

Lizmap will then:

• Use the DynamicLayers server plugin to create a child project
• Copy and adapt the Lizmap configuration of the parent project for the child project ( global and layers extent, etc.)
• Redirect to the new map, for example to

http://lizmap.localhost/index.php/view/map/?repository=somerepo&project=someproject__variable_source_idIN3

This way you can spend time creating a beautiful map for you parent project, publish it via Lizmap, and then automatically publish many child projects as derivated map, with no effort !

Michaël DOUCHIN ( 3liz.com ) - @mdouchin

Originally funded by Dyopta, France http://www.dyopta.com/

GPL V2