Configurando as aplicações externas¶

SAGA¶

SAGA algorithms can be run from QGIS if you have SAGA installed in your system and you configure the processing framework properly so it can find SAGA executables. In particular, the SAGA command-line executable is needed to run SAGA algorithms.

If you are running Windows, both the stand-alone installer and the OSGeo4W installer include SAGA along with QGIS, and the path is automatically configured, so there is no need to do anything else.

If you have installed SAGA yourself (remember, you need version 2.1), the path to the SAGA executable must be configured. To do this, open the configuration dialog. In the SAGA block, you will find a setting named SAGA Folder. Enter the path to the folder where SAGA is installed. Close the configuration dialog, and now you are ready to run SAGA algorithms from QGIS.

If you are running Linux, SAGA binaries are not included with SEXTANTE, so you have to download and install the software yourself. Please check the SAGA website for more information. SAGA 2.1 is needed.

In this case, there is no need to configure the path to the SAGA executable, and you will not see those folders. Instead, you must make sure that SAGA is properly installed and its folder is added to the PATH environment variable. Just open a console and type saga_cmd to check that the system can find where the SAGA binaries are located.

R. Creating R scripts¶

R integration in QGIS is different from that of SAGA in that there is not a predefined set of algorithms you can run (except for a few examples). Instead, you should write your scripts and call R commands, much like you would do from R, and in a very similar manner to what we saw in the section dedicated to processing scripts. This section shows you the syntax to use to call those R commands from QGIS and how to use QGIS objects (layers, tables) in them.

The first thing you have to do, as we saw in the case of SAGA, is to tell QGIS where your R binaries are located. You can do this using the R folder entry in the processing configuration dialog. Once you have set that parameter, you can start creating and executing your own R scripts.

Uma vez mais, isto é diferente no Linux, e só tem de ter certeza que a pasta do R está incluída na variável de ambiente PATH. Se conseguir iniciar o R, apenas introduza R na consola, e estará pronto a começar.

To add a new algorithm that calls an R function (or a more complex R script that you have developed and you would like to have available from QGIS), you have to create a script file that tells the processing framework how to perform that operation and the corresponding R commands to do so.

Os arquivos de script R têm a extensão .rsx e é fácil criá-los se tiver o conhecimento básico da sintaxe do R e do código R. Eles devem ficar armazenados na pasta scripts R. Pode definir esta pasta no grupo de configurações R (disponível a partir do diálogo de configurações do processamento), como faz com a pasta para scripts normais do processamento.

Let’s have a look at a very simple script file, which calls the R method spsample to create a random grid within the boundary of the polygons in a given polygon layer. This method belongs to the maptools package. Since almost all the algorithms that you might like to incorporate into QGIS will use or generate spatial data, knowledge of spatial packages like maptools and, especially, sp, is mandatory.

##polyg=vector
##numpoints=number 10
##output=output vector
##sp=group
pts=spsample(polyg,numpoints,type="random")
output=SpatialPointsDataFrame(pts, as.data.frame(pts))

The first lines, which start with a double Python comment sign (##), tell QGIS the inputs of the algorithm described in the file and the outputs that it will generate. They work with exactly the same syntax as the SEXTANTE scripts that we have already seen, so they will not be described here again.

When you declare an input parameter, QGIS uses that information for two things: creating the user interface to ask the user for the value of that parameter and creating a corresponding R variable that can later be used as input for R commands.

In the above example, we are declaring an input of type vector named polyg. When executing the algorithm, QGIS will open in R the layer selected by the user and store it in a variable also named polyg. So, the name of a parameter is also the name of the variable that we can use in R for accesing the value of that parameter (thus, you should avoid using reserved R words as parameter names).

Spatial elements such as vector and raster layers are read using the readOGR() and brick() commands (you do not have to worry about adding those commands to your description file – QGIS will do it), and they are stored as Spatial*DataFrame objects. Table fields are stored as strings containing the name of the selected field.

Tabelas são abertas usando o comando read.csv(). Se uma tabela inserida pelo usuário não está no formato CSV, será convertida antes de importá-la para R.

Adicionalmente, os arquivos raster pode ser lidos usando o comando readGDAL() em vez de brick(), usando o ##usereadgdal.

If you are an advanced user and do not want QGIS to create the object representing the layer, you can use the ##passfilename tag to indicate that you prefer a string with the filename instead. In this case, it is up to you to open the file before performing any operation on the data it contains.

Com a informação em cima, podemos agora perceber a primeira linha do nosso primeiro script exemplo (a primeira linha que não começa com o comentário Python).

pts=spsample(polyg,numpoints,type="random")

A variável polygon já contém o objecto SpatialPolygonsDataFrame, portanto pode ser usado para chamar o método spsample, tal como o numpoints, que indica o número de pontos a ser adicionados ao grid de amostra criada.

Desde que declarado uma saída do tipo vetor chamado out, temos que criar uma variável chamada out e armazenar um ` Spatial*DataFrame objeto nele (neste caso, um SpatialPointsDataFrame). Você pode usar qualquer nome para as variáveis ​​intermediárias. Apenas certifique-se de que a variável que armazena o resultado final tem o mesmo nome que você usou para declará-la, e que contém um valor adequado.

In this case, the result obtained from the spsample method has to be converted explicitly into a SpatialPointsDataFrame object, since it is itself an object of class ppp, which is not a suitable class to be returned to QGIS.

Se o seu algoritmo gera camadas raster, a maneira como eles são salvos vai depender se você tem usado ou não usou a opção `` #dontuserasterpackag . O que você tem usado, as camadas são salvas usando o método `` writeGDAL () ``. Se não, o `` writeRaster () `` método do pacote de  ``raster será usado.

Se usou a opção #passfilename, os arquivos de saída são gerados usando o pacote raster (com writeRaster()), mesmo que não seja usado nos arquivos de entrada.

Se o seu algoritmo não gera qualquer camada, mas sim um resultado de texto no console em vez disso, você tem que indicar que deseja que o console seja exibido uma vez que a execução seja concluída. Para isso, basta começar as linhas de comando que produzem os resultados que você deseja imprimir com a > (‘greater’) sign. A saída de todas as outras linhas não serão mostradas. Por exemplo, aqui está o arquivo de descrição de um algoritmo que realiza um teste de normalidade em um determinado campo (coluna) dos atributos de uma camada vetorial:

##layer=vector
##field=field layer
##nortest=group
library(nortest)
>lillie.test(layer[[field]])

The output of the last line is printed, but the output of the first is not (and neither are the outputs from other command lines added automatically by QGIS).

Se o seu algoritmo criar qualquer tipo de gráficos (usando o método ``plot()), adicione a seguinte linha:

##showplots

This will cause QGIS to redirect all R graphical outputs to a temporary file, which will be opened once R execution has finished.

Tanto os gráficos como os resultados do console serão exibidos no gestor de resultados do processamento.

For more information, please check the script files provided with SEXTANTE. Most of them are rather simple and will greatly help you understand how to create your own scripts.

GRASS¶

Configuring GRASS is not much different from configuring SAGA. First, the path to the GRASS folder has to be defined, but only if you are running Windows. Additionaly, a shell interpreter (usually msys.exe, which can be found in most GRASS for Windows distributions) has to be defined and its path set up as well.

By default, the processing framework tries to configure its GRASS connector to use the GRASS distribution that ships along with QGIS. This should work without problems in most systems, but if you experience problems, you might have to configure the GRASS connector manually. Also, if you want to use a different GRASS installation, you can change that setting and point to the folder where the other version is installed. GRASS 6.4 is needed for algorithms to work correctly.

Se está a trabalhar em Linux, só necessita de ter a certeza que o GRASS está corretamente instalado, e pode ser executado sem problema a partir do console.

GRASS algorithms use a region for calculations. This region can be defined manually using values similar to the ones found in the SAGA configuration, or automatically, taking the minimum extent that covers all the input layers used to execute the algorithm each time. If the latter approach is the behaviour you prefer, just check the Use min covering region option in the GRASS configuration parameters.

The last parameter that has to be configured is related to the mapset. A mapset is needed to run GRASS, and the processing framework creates a temporary one for each execution. You have to specify if the data you are working with uses geographical (lat/lon) coordinates or projected ones.

GDAL¶

No additional configuration is needed to run GDAL algorithms. Since they are already incorporated into QGIS, the algorithms can infer their configuration from it.

Orfeo Toolbox¶

Orfeo Toolbox (OTB) algorithms can be run from QGIS if you have OTB installed in your system and you have configured QGIS properly, so it can find all necessary files (command-line tools and libraries).

As in the case of SAGA, OTB binaries are included in the stand-alone installer for Windows, but they are not included if you are runing Linux, so you have to download and install the software yourself. Please check the OTB website for more information.

Once OTB is installed, start QGIS, open the processing configuration dialog and configure the OTB algorithm provider. In the Orfeo Toolbox (image analysis) block, you will find all settings related to OTB. First, ensure that algorithms are enabled.

Em seguida, configure o caminho para a pasta onde estão as ferramentas da linha de comandos OTB e as bibliotecas estão instaladas:

• normalmente OTB applications folder encaminha para /usr/lib/otb/applications e OTB command line tools folder é /usr/bin

• If you use the OSGeo4W installer, then install otb-bin package and enter C:\OSGeo4W\apps\orfeotoolbox\applications as OTB applications folder and C:\OSGeo4W\bin as OTB command line tools folder. These values should be configured by default, but if you have a different OTB installation, configure them to the corresponding values in your system.

TauDEM¶

To use this provider, you need to install TauDEM command line tools.