28.1.9. Modeler tools

Warning

These tools are only available in the model designer. They are not available in the Processing Toolbox.

28.1.9.1. Calculate expression

It calculates the result of a QGIS expression and eliminates the need to use the same expression multiple times throughout a model when the same result is required more than once. Additionally, it enables use cases that would otherwise not be possible. For instance, you can generate a timestamp value once and use it multiple times within the model, if the timestamp were recalculated every time, the values would vary during the model’s runtime.

Parameters

Label	Name	Type	Description
Input	INPUT	[expression]	Expression to calculate

Outputs

Label	Name	Type	Description
Value	OUTPUT	[Result Value]	Calculated result value, the data type of the output will vary based on the specific expression used in the algorithm.

Python code

Algorithm ID: native:calculateexpression

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.9.2. Conditional branch

Adds a conditional branch into a model, allowing parts of the model to be executed based on the result of an expression evaluation. Mostly by using tool dependencies to control the flow of a model.

Parameters

Label	Name	Type	Description
Field	BRANCH	[string]	Name of the condition
Field	CONDITION	[expression]	Expression to evaluate

Outputs

None.

Python code

Algorithm ID: native:condition

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.9.3. Create directory

Creates a new directory on a file system. Directories will be created recursively, creating all required parent directories in order to construct the full specified directory path. No errors will be raised if the directory already exists.

Parameters

Label	Name	Type	Description
Directory path	PATH	[string]	Folder path to create

Outputs

Label	Name	Type	Description
Output	OUTPUT	[folder]	Created folder

Python code

Algorithm ID: native:createdirectory

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.9.4. Feature filter

Filters features from the input layer and redirects them to one or several outputs. If you do not know about any attribute names that are common to all possible input layers, filtering is only possible on the feature geometry and general record mechanisms, such as $id and uuid.

Parameters

Label	Name	Type	Description
Input layer	INPUT	[vector: any]	The input layer.
Outputs and filters (one or more)	OUTPUT_<name of the filter>	[same as input]	The output layers with filters (as many as there are filters).

Outputs

Label	Name	Type	Description
Output (one or more)	native:filter_1:OUTPUT_<name of filter>	[same as input]	The output layers with filtered features (as many as there are filters).

Python code

Algorithm ID: native:filter

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.9.5. Filter layers by type

Filters layers by their type. Incoming layers will be directed to different outputs based on whether they are a vector or raster layer.

Parameters

Label	Name	Type	Description
Input layer	INPUT	[layer]	Generic Map Layer

Outputs

Label	Name	Type	Description
Vector features Optional	VECTOR	[vector]	A Vector Layer of the input, if compatible
Raster layer Optional	RASTER	[raster]	A Raster Layer of the input, if compatible

Python code

Algorithm ID: native:filterlayersbytype

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.9.6. Load layer into project

Loads a layer to the current project.

Parameters

Label	Name	Type	Description
Layer	INPUT	[layer]	Layer to load in the legend
Loaded layer name	NAME	[string]	Name of the loaded layer

Outputs

Label	Name	Type	Description
Layer	OUTPUT	[same as input]	The (renamed) loaded layer

Python code

Algorithm ID: native:loadlayer

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.9.7. Raise exception

Raises an exception and cancels a model’s execution. The exception message can be customized, and optionally an expression based condition can be specified. If an expression condition is used, then the exception will only be raised if the expression result is true. A false result indicates that no exception will be raised, and the model execution can continue uninterrupted.

Parameters

Label	Name	Type	Description
Message	MESSAGE	[string]	Message to display
Condition Optional	CONDITION	[expression]	Expression to evaluate if true

Outputs

A message in the log panel.

Python code

Algorithm ID: native:raiseexception

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.9.8. Raise message

Raises an information message in the log. The message can be customized, and optionally an expression based condition can be specified. If an expression condition is used, then the message will only be logged if the expression result is true. A false result indicates that no message will be logged.

Parameters

Label	Name	Type	Description
Information message	MESSAGE	[string]	Message to display
Condition Optional	CONDITION	[expression]	Expression to evaluate if true

Outputs

A message in the log panel.

Python code

Algorithm ID: native:raisemessage

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.9.9. Raise warning

Raises a warning message in the log. The warning message can be customized, and optionally an expression based condition can be specified. If an expression condition is used, then the warning will only be logged if the expression result is true. A false result indicates that no warning will be logged.

Parameters

Label	Name	Type	Description
Message	MESSAGE	[string]	Message to display
Condition Optional	CONDITION	[expression]	Expression to evaluate if true

Outputs

A message in the log panel.

Python code

Algorithm ID: native:raisewarning

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.9.10. Rename layer

Renames a layer.

Parameters

Label	Name	Type	Description
Layer	INPUT	[layer]	Layer to rename
New name	NAME	[string]	The new name of the layer

Outputs

Label	Name	Type	Description
Layer	OUTPUT	[same as input]	The (renamed) output layer

Python code

Algorithm ID: native:renamelayer

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.9.11. Save log to file

Saves the model’s execution log to a file. Optionally, the log can be saved in a HTML formatted version.

Parameters

Label	Name	Type	Description
Use HTML	USE_HTML	[Boolean] Default: False	Use HTML formatting

Outputs

Label	Name	Type	Description
File	OUTPUT	[string]	Destination of the log

Python code

Algorithm ID: native:savelog

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.9.12. Set project variable

Sets an expression variable for the current project.

Parameters

Label	Name	Type	Description
Variable name	NAME	[string]	Name of the variable
Variable value	VALUE	[string]	Value to be stored

Outputs

None.

Python code

Algorithm ID: native:setprojectvariable

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.9.13. String concatenation

Concatenates two strings into a single one in the Processing Modeler.

Parameters

Label	Name	Type	Description
Input 1	INPUT_1	[string]	First string
Input 2	INPUT_2	[string]	Second string

Outputs

Label	Name	Type	Description
Concatenation	CONCATENATION	[string]	The concatenated string

Python code

Algorithm ID: native:stringconcatenation

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.9.14. Variable distance buffer

Warning

This algorithm is deprecated and can be removed anytime. Prefer using Buffer algorithm instead.

Computes a buffer area for all the features in an input layer.

The size of the buffer for a given feature is defined by an attribute, so it allows different features to have different buffer sizes.

See also

Buffer

Parameters

Label	Name	Type	Description
Input layer	INPUT	[vector: any]	Input vector layer
Distance field	DISTANCE	[tablefield: numeric]	Attribute for the distance radius of the buffer
Segments	SEGMENTS	[number] Default: 5	Controls the number of line segments to use to approximate a quarter circle when creating rounded offsets.
Dissolve result	DISSOLVE	[boolean] Default: False	Choose to dissolve the final buffer, resulting in a single feature covering all input features. Fig. 28.8 Normal and dissolved buffer
End cap style	END_CAP_STYLE	[enumeration] Default: Round	Controls how line endings are handled in the buffer. Fig. 28.9 Round, flat and square cap styles
Join style	JOIN_STYLE	[enumeration] Default: Round	Specifies whether round, miter or beveled joins should be used when offsetting corners in a line.
Miter limit	MITER_LIMIT	[number] Default: 2.0	Only applicable for mitered join styles, and controls the maximum distance from the offset curve to use when creating a mitered join.

Outputs

Label	Name	Type	Description
Buffer	OUTPUT	[vector: polygon]	Buffer polygon vector layer.

Python code

Algorithm ID: qgis:variabledistancebuffer

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.