{"id":5327,"date":"2018-05-21T21:13:48","date_gmt":"2018-05-21T19:13:48","guid":{"rendered":"http:\/\/www.sigterritoires.fr\/?p=5327"},"modified":"2018-10-17T12:50:44","modified_gmt":"2018-10-17T10:50:44","slug":"processing-algorithms-in-the-qgis-2-8-graphic-modeler","status":"publish","type":"post","link":"https:\/\/www.sigterritoires.fr\/index.php\/en\/processing-algorithms-in-the-qgis-2-8-graphic-modeler\/","title":{"rendered":"Processing algorithms in the QGis 2.8 Graphic Modeler"},"content":{"rendered":"

Adding<\/strong>\u00a0Algorithms in the Graphic Modeler<\/strong><\/p>\n

The algorithms are added in\u00a0\u00a0\u00a0the graphical modeler in the same way as the input data. You simply select the tab\u00a0\u00a0\u00a0algorithms<\/em><\/strong>\u00a0\u00a0<\/em>\u00a0instead of the tab\u00a0\u00a0\u00a0Inputs<\/em><\/strong>, to see the display corresponding to the panel\u00a0\u00a0\u00a0Toolbox of treatments<\/em><\/strong>\u00a0.<\/p>\n

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Once you have found the algorithm you want to add, double-click on it, or drag it to the Modeler graphic window.\u00a0In order to find the algorithm, you just research in the Processing Toolbox, typing the name in the search box at the top of the algorithm tab.<\/p>\n

In fact, the tab\u00a0\u00a0\u00a0algorithms<\/em><\/strong>\u00a0\u00a0<\/em>\u00a0is the opened window of the toolbox in the modeler.\u00a0The display of this box has two parameters: Advanced and Simplified.<\/p>\n

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Display with advance interface<\/p>\n

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Display with simplified interface<\/p>\n

The parameter of the interface that is currently used in the processing toolbox determines how the algorithms will be organized in the graphical modeler.\u00a0This parameter cannot be changed in the graphical modeler.\u00a0To change the setting, the graphical modeler must be stopped, the interface parameter must be changed in the toolbox and the graphical modeler must be restarted. Apart from that, finding algorithms follows the same approach as in the treatment toolbox: type the name or a part of the name of the desired treatment and you will have the list of available treatments.<\/p>\n

In the algorithms tab, there is a special category called\u00a0\u00a0\u00a0Modeler specific tools<\/em><\/strong>.\u00a0The three tools – Calculator, Raster Layers Limits, and Vector Layers Limits – do not appear in the toolbox.\u00a0These are tools that make sense only when used as part of the graphical modeler.<\/p>\n

The calculator tool is\u00a0\u00a0\u00a0the most commonly used of the three tools.\u00a0It allows you to perform arithmetic calculations on the digital outputs of other algorithms, and to insert them as input to other treatments of the same model.<\/p>\n

When you add the calculator to the graphics window, the info window\u00a0\u00a0\u00a0lists the\u200b\u200bavailable digital values \u200b\u200b within the model.\u00a0The window below is used to enter a calculation formula by using the letters assigned to each numerical value as variables.\u00a0For example, the formula entered\u00a0\u00a0\u00a0in the following figure\u00a0\u00a0\u00a0displays the only digital variable of our current model (the buffer distance) and calculates twice that distance (a * 2).<\/p>\n

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This output can be used as input to another algorithm of this model.<\/p>\n

When you add an algorithm to the graphical window of the modeler, the parameter window of the algorithm opens.\u00a0The dialog box will be very similar to the one you would have if you had launched the tool directly from the processing box:\u00a0you will have the input data, the output data and the tool parameters.<\/p>\n

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However, there are some important differences since the graphical modeler is an autonomous universe of data entries.\u00a0The differences are the following:
\n\u2022 In the list of\u00a0\u00a0\u00a0input layers<\/em><\/strong>\u00a0\u00a0\u00a0you will be limited to those that have been added to the template.<\/p>\n

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\n\u2022 The field\u00a0\u00a0\u00a0Exit<\/em><\/strong>\u00a0\u00a0<\/em>\u00a0can be left empty if it is an intermediate result that will be used as input for another algorithm.\u00a0If the output is a layer that needs to be saved, enter the name of that layer in the text box.\u00a0When you name an output layer, you do not need to provide an output file name.\u00a0This will be done when the tool is run.\u00a0Instead, just enter the name of the layer (for example,\u00a0buffer installations<\/em>).
\nIt is important to understand how the output data of an algorithm works:<\/p>\n