QGIS User Guide - QGIS Documentation [PDF]

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QGIS User Guide Version 2.8

QGIS Project

30 July 2016

Contents

1

Préambule

3

2

Conventions 2.1 Conventions pour les éléments d’interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Text or Keyboard Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Instructions spécifiques à un système d’exploitation . . . . . . . . . . . . . . . . . . . . . . . .

5 5 5 6

3

Avant-propos

7

4

Fonctionnalités 4.1 Visualiser des données . . . . . . . . . . . 4.2 Parcourir les données et créer des cartes . . 4.3 Créer, éditer, gérer et exporter des données 4.4 Analyse ; imagerelpath="images/test_image.jpg"; projectpath=qgis.core.QgsProject.instance().fileName(); import os.path; path=os.path.dirname(str(projectpath)) if projectpath != ’’ else None; image=os.path.join(path, imagerelpath); import subprocess; subprocess.Popen( [command, image ] );

Un autre exemple d’action Python consiste à ajouter de nouvelles couche au projet. L’exemple qui suit montre comment ajouter une couche vecteur et un raster. Les noms des fichiers à ajouter au projet et les noms à donner aux couches dépendent de données attributaires (filename et layername sont deux champs de la table attributaire de la couche sur laquelle l’action est créée) : qgis.utils.iface.addVectorLayer(’/yourpath/[% "filename" %].shp’,’[% "layername" %]’, ’ogr’)

Pour ajouter un raster (ici une image TIF), cela devient : qgis.utils.iface.addRasterLayer(’/yourpath/[% "filename" %].tif’,’[% "layername" %] ’)

12.3.8 Onglet Jointures The Joins menu allows you to join a loaded attribute table to a loaded vector layer. After clicking , the Add vector join dialog appears. As key columns, you have to define a join layer you want to connect with the target vector layer. Then, you have to specify the join field that is common to both the join layer and the target layer. Now you can also specify a subset of fields from the joined layer based on the checkbox Choose which fields are joined. As a result of the join, all information from the join layer and the target layer are displayed in the attribute table of the target layer as joined information. If you specified a subset of fields only these fields are displayed in the attribute table of the target layer. QGIS currently has support for joining non-spatial table formats supported by OGR (e.g., CSV, DBF and Excel), delimited text and the PostgreSQL provider (see figure_joins_1). De plus, la fenêtre de jointure vous permet de : •

Mettre la couche jointe en cache dans la mémoire virtuelle

12.3. Fenêtre Propriétés d’une couche vecteur

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Figure 12.36: Join an attribute table to an existing vector layer



Créer un index des attributs joins



Choisir les champs à joindre



Personnaliser le préfixe du champ

12.3.9 Onglet Diagrammes L’onglet Diagrammes permet d’ajouter une couche de graphiques sur une couche vecteur (voir figure_diagrams_1). The current core implementation of diagrams provides support for pie charts, text diagrams and histograms. The menu is divided into four tabs: Appearance, Size, Postion and Options. In the cases of the text diagram and pie chart, text values of different , group=’Custom’) def myfunc(value1, value2 feature, parent): pass

The short example creates a function ‘myfunc’ that will give you a function with two values. When using the args=’auto’ function argument the number of function arguments required will be calculated by the number of arguments the function has been defined with in Python (minus 2 - feature, and parent). This function then can be used with the following expression: myfunc(’test1’, ’test2’)

Your function will be implemented in the ‘Custom’ Functions of the Expression tab after using the Run Script button.

Further information about creating Python code can be found on http://www.qgis.org/html/en/docs/pyqgis_developer_cookbook/inde The function editor is not only limited to working with the field calculator, it can be found whenever you work with expressions. See also Expressions. .

12.7. Calculatrice de champ

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138

Chapter 12. Les données vectorielles

CHAPTER 13

Les données raster

.

13.1 Les données raster This section describes how to visualize and set raster layer properties. QGIS uses the GDAL library to read and write raster , ATTRS{idProduct}=="0003", MODE="666"

Après cela il est nécessaire de s’assurer que le module du noyau garmin_gps n’est pas chargé rmmod garmin_gps

vous pouvez alors utiliser les Outils GPS. Malheureusement il semble y avoir un bug #7182 et généralement QGIS se bloque plusieurs fois avant que l’opération ne réussisse. BTGP-38KM encoding="UTF-8"?>

The parser reads this definition and creates a new tab inside the Toolbox when you select the module. A more detailed description for adding new modules, changing a module’s group, etc., can be found on the QGIS wiki at http://hub.qgis.org/projects/quantum-gis/wiki/Adding_New_Tools_to_the_GRASS_Toolbox. .

16.9. La Boîte à outils GRASS

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194

Chapter 16. Intégration du SIG GRASS

CHAPTER 17

QGIS processing framework

.

17.1 Introduction This chapter introduces the QGIS processing framework, a geoprocessing environment that can be used to call native and third-party algorithms from QGIS, making your spatial analysis tasks more productive and easy to accomplish. Dans les sections suivantes, seront exposés les éléments graphiques de ce module et comment les exploiter au maximum. There are four basic elements in the framework GUI, which are used to run algorithms for different purposes. Choosing one tool or another will depend on the kind of analysis that is to be performed and the particular characteristics of each user and project. All of them (except for the batch processing interface, which is called from the toolbox, as we will see) can be accessed from the Processing menu item. (You will see more than four entries. The remaining ones are not used to execute algorithms and will be explained later in this chapter.) • La Boîte à outils. Il s’agit de l’élément principal de l’interface du module de Traitements et permet de lancer les algorithmes individuellement ou par lot.

Figure 17.1: Processing Toolbox

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• Le modeleur graphique. Les algorithmes peuvent être combinés graphiquement en utilisant le modeleur pour définir une chaîne de traitements, composée de plusieurs étapes de traitement

Figure 17.2: Processing Modeler • Le gestionnaire d’historiques. Toutes les actions réalisées par un élément précité sont sauvegardées dans un fichier d’historique et peuvent être aisément reproduites grâce au gestionnaire d’historiques. • Le gestionnaire de traitement par lot. Cette interface permet d’exécuter des traitements par lots et d’automatiser l’exécution d’un même traitement sur plusieurs sources de données. Dans les sections suivantes, chacun de ces éléments sera détaillé. .

17.2 La boîte à outils La Boîte à outils est l’élément principal du module de Traitements et probablement celui que vous utiliserez le plus au quotidien. Elle montre la liste des algorithmes disponibles, regroupés en plusieurs catégories. C’est aussi par son intermédiaire qu’il est possible d’exécuter un algorithme sur un jeu de données en entrée, ponctuellement ou par lot. The toolbox contains all the available algorithms, divided into predefined groups. All these groups are found under a single tree entry named Geoalgorithms. Additionally, two more entries are found, namely Models and Scripts. These include user-created algorithms, and they allow you to define your own workflows and processing tasks. We will devote a full section to them a bit later. Dans la partie haute de la boîte à outils se trouve un champ texte. Pour réduire le nombre d’algorithmes affichés dans la boîte à outils et vous permettre de trouver celui qui vous convient, il vous suffit d’entrer un mot-clé ou une phrase dnas ce champ. La liste des algorithmes contenant ce texte est filtrée au fur et à mesure de la saisie. In the lower part, you will find a box that allows you to switch between the simplified algorithm list (the one explained above) and the advanced list. If you change to the advanced mode, the toolbox will look like this:

196

Chapter 17. QGIS processing framework

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Figure 17.3: Processing History

Figure 17.4: Batch Processing interface

17.2. La boîte à outils

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Figure 17.5: Processing Toolbox

Figure 17.6: Processing Toolbox (advanced mode)

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In the advanced view, each group represents a so-called ‘algorithm provider’, which is a set of algorithms coming from the same source, for instance, from a third-party application with geoprocessing capabilities. Some of these groups represent algorithms from third-party applications like SAGA, GRASS or R, while others contain algorithms directly coded as part of the processing plugin, not relying on any additional software. This view is recommended to those users who have a certain knowledge of the applications that are backing the algorithms, since they will be shown with their original names and groups. Also, some additional algorithms are available only in the advanced view, such as LiDAR tools and scripts based on the R statistical computing software, among others. Independent QGIS plugins that add new algorithms to the toolbox will only be shown in the advanced view. In particular, the simplified view contains algorithms from the following providers: • GRASS • SAGA • OTB • Native QGIS algorithms In the case of running QGIS under Windows, these algorithms are fully-functional in a fresh installation of QGIS, and they can be run without requiring any additional installation. Also, running them requires no prior knowledge of the external applications they use, making them more accesible for first-time users. If you want to use an algorithm not provided by any of the above providers, switch to the advanced mode by selecting the corresponding option at the bottom of the toolbox. Pour exécuter un algorithme, double-cliquez simplement sur son nom dans la boîte à outils.

17.2.1 La fenêtre Algorithme Once you double-click on the name of the algorithm that you want to execute, a dialog similar to that in the figure below is shown (in this case, the dialog corresponds to the SAGA ‘Convergence index’ algorithm).

Figure 17.7: Parameters Dialog This dialog is used to set the input values that the algorithm needs to be executed. It shows a table where input values and configuration parameters are to be set. It of course has a different content, depending on the require17.2. La boîte à outils

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ments of the algorithm to be executed, and is created automatically based on those requirements. On the left side, the name of the parameter is shown. On the right side, the value of the parameter can be set. Les algorithmes différeront par le nombre et le type de paramètres, mais la structure sera la même pour tous. Les paramètres présents dans la table pourront être un des types suivants. • A raster layer, to select from a list of all such layers available (currently opened) in QGIS. The selector contains as well a button on its right-hand side, to let you select filenames that represent layers currently not loaded in QGIS. • A vector layer, to select from a list of all vector layers available in QGIS. Layers not loaded in QGIS can be selected as well, as in the case of raster layers, but only if the algorithm does not require a table field selected from the attributes table of the layer. In that case, only opened layers can be selected, since they need to be open so as to retrieve the list of field names available. Vous verrez un bouton pour chaque sélecteur de couche de vecteur, comme le montre la figure ci-dessous.

Figure 17.8: Vector iterator button Si l’algorithme propose plusieurs boutons d’itération, vous ne pourrez en activer qu’un seul. Si un bouton correspondant à une couche vecteur est activé, l’algorithme s’exécutera successivement sur chacune des entités de la couche plutôt que sur la couche en entier, produisant alors autant de sorties que de nombre d’exécution de l’algorithme. Cela permet d’automatiser un traitement qui doit être réalisé sur chaque entité d’une couche séparément. • A table, to select from a list of all available in QGIS. Non-spatial tables are loaded into QGIS like vector layers, and in fact they are treated as such by the program. Currently, the list of available tables that you will see when executing an algorithm that needs one of them is restricted to tables coming from files in dBase (.dbf) or Comma-Separated Values (.csv) formats. • Une option, à choisir dans une liste d’options possibles. • A numerical value, to be introduced in a text box. You will find a button by its side. Clicking on it, you will see a dialog that allows you to enter a mathematical expression, so you can use it as a handy calculator. Some useful variables related to ) output=SpatialPoints)

La variable polygon contient déjà un objet SpatialPolygons?> Import all photograph points This command will import all of the encoding="UTF-8"?>

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