![]() ![]() Processing can then setup the algorithm, prepare the input datasets, execute the algorithm and later process the resulting outputs. Once the algorithm is implemented, it is added to the list of available algorithms. Outputs are stored in the locations specified by the user-defined output configuration (at the moment, only file output is supported). This method must take the values of the algorithm input parameters (which have been set by the user through any of the UI elements of processing, such as the toolbox, batch processing interface, etc.) to compute outputs. This makes is easier to adapt to new versions of the backend software, where algorithms might have changed, since the necessary adaptations are limited to changes in the description files and no Processing code has to be rewritten.Īs the second step, the algorithm code, which will use the inputs provided to the algorithms and produce the outputs, is implemented in the processAlgorithm() method. This is done to simplify the process of adding the large collections of algorithms that these backends provide by taking advantage of the fact that most of them provide some mechanism of describing their algorithms. Instead, defineCharacteristics() reads the input and output descriptions from a file and uses that information to populate the input and output arrays. In some cases, for example, where algorithms use a backend, such as GRASS or SAGA, parameters are not directly defined in these methods. Additional parameters that describe the algorithm, such as the name of the associated group, are also defined in this method. ![]() These should be included in the defineCharacteristics() method, which populates the arrays of inputs and outputs, defining the semantics of the algorithm. More specifically, the implementation of algorithms in the GeoAlgorithm class involves two main steps: first, the inputs required by the algorithm and the outputs that it will produce are specified. This effect, an increasing number of contributions, has been very noticeable since the introduction of the QGIS Python API in QGIS 0.9 in 2007 when new developers started to add functionality using Python plugins. As note, a “powerful Python interface can help to efficiently exploit the capabilities of a GIS” and integrate different tools and programming languages to expand it. Additionally, QGIS provides a Python application program interface (API), which is used to expand its functionality. The QGIS core is developed using the Qt toolkit and C++. QGIS runs on most Linux and Unix platforms, Windows and Mac OS X and has been published under the GNU (a collection of free software the acronym stands for “GNU’s not Unix”) General Public License (GPL). Today, QGIS has reached a point in its evolution where it is used by a wide variety of users for daily spatial data viewing, editing, and analysis tasks, as well as in education (for example, ). The initial goal of the QGIS project was to create a spatial data viewer. QGIS is an open source GIS project, which was started in 2002. ![]()
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