:orphan:

.. _algs_include:

*******************
Algorithms Include
*******************

.. only:: html

   .. contents::
      :local:
      :depth: 1


Python Code Sample
==================

The following section is used to load python code sample in algs help

**algorithm_code_section**

.. code-block:: python

    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 :ref:`processing_console` for details on how to run processing algorithms
from the Python console.

**end_algorithm_code_section**


Output Types
============

The following describes the different options for algorithm outputs,
with variants including the "skip output" and the "append" options

Directory
---------

**directory_output_types**

* Save to a Temporary Directory
* Save to Directory

**end_directory_output_types**


**directory_output_types_skip**

* Skip Output
* Save to a Temporary Directory
* Save to Directory

**end_directory_output_types_skip**

File
----

**file_output_types**

* Save to a Temporary File
* Save to File…

**end_file_output_types**


**file_output_types_skip**

* Skip Output
* Save to a Temporary File
* Save to File…

**end_file_output_types_skip**

Layer
-----

**layer_output_types**

* Create Temporary Layer (``TEMPORARY_OUTPUT``)
* Save to File…
* Save to Geopackage…
* Save to Database Table…

The file encoding can also be changed here.

**end_layer_output_types**


**layer_output_types_append**

* Create Temporary Layer (``TEMPORARY_OUTPUT``)
* Save to File…
* Save to Geopackage…
* Save to Database Table…
* Append to Layer…

The file encoding can also be changed here.

**end_layer_output_types_append**


**layer_output_types_skip**

* Skip Output
* Create Temporary Layer (``TEMPORARY_OUTPUT``)
* Save to File…
* Save to Geopackage…
* Save to Database Table…

The file encoding can also be changed here.

**end_layer_output_types_skip**


Extent Dropdown
===============

The following refers to the extent selector widget in the algorithms GUI

**extent_options**

Available methods are:

* Calculate from layer…: uses extent of a layer loaded in the current project
* Use map canvas extent
* Draw on canvas
* Enter the coordinates as ``xmin, xmax, ymin, ymax``

**end_extent_options**


Geometric predicates
====================

The following section is included in vector selection algorithms such as
qgisselectbylocation, qgisextractbylocation and vector general algorithms
such as qgisjoinattributesbylocation and qgisjoinbylocationsummary

**geometric_predicates**

Geometric predicates are boolean functions used to determine the spatial
relation a feature has with another by comparing whether and how
their geometries share a portion of space.

.. figure:: /docs/user_manual/processing_algs/img/selectbylocation.png
   :align: center

   Looking for spatial relations between layers

Using the figure above, we are looking for the green circles by spatially
comparing them to the orange rectangle feature.
Available geometric predicates are:

*Intersect*
  Tests whether a geometry intersects another. Returns 1 (true) if the
  geometries spatially intersect (share any portion of space - overlap or touch) and 0 if they
  don’t. In the picture above, this will return circles 1, 2 and 3.

*Contain*
  Returns 1 (true) if and only if no points of b lie in the exterior of a,
  and at least one point of the interior of b lies in the interior of a.
  In the picture, no circle is returned, but the rectangle would be if you
  would look for it the other way around, as it contains circle 1 completely.
  This is the opposite of *are within*.

*Disjoint*
  Returns 1 (true) if the geometries do not share any portion of space (no overlap, not touching).
  Only circle 4 is returned.

*Equal*
  Returns 1 (true) if and only if geometries are exactly the same.
  No circles will be returned.

*Touch*
  Tests whether a geometry touches another. Returns 1 (true) if the geometries
  have at least one point in common, but their interiors do not intersect.
  Only circle 3 is returned.

*Overlap*
  Tests whether a geometry overlaps another. Returns 1 (true) if the geometries
  share space, are of the same dimension, but are not completely contained by
  each other. Only circle 2 is returned.

*Are within*
  Tests whether a geometry is within another. Returns 1 (true) if geometry a
  is completely inside geometry b. Only circle 1 is returned.

*Cross*
  Returns 1 (true) if the supplied geometries have some, but not all, interior
  points in common and the actual crossing is of a lower dimension than the
  highest supplied geometry. For example, a line crossing a polygon will cross
  as a line (true). Two lines crossing will cross as a point (true).
  Two polygons cross as a polygon (false).
  In the picture, no circles will be returned.

**end_geometric_predicates**