소개¶

PYQGIS_STARTUP 환경 변수¶

You can run Python code just before QGIS initialization completes by setting the PYQGIS_STARTUP environment variable to the path of an existing Python file.

This method is something you will probably rarely need, but worth mentioning here because it is one of the several ways to run Python code within QGIS and because this code will run before QGIS initialization is complete. This method is very useful for cleaning sys.path, which may have undesireable paths, or for isolating/loading the initial environ without requiring a virt env, e.g. homebrew or MacPorts installs on Mac.

startup.py 파일¶

Every time QGIS starts, the user’s Python home directory (usually: .qgis2/python) is searched for a file named startup.py, if that file exists, it is executed by the embedded Python interpreter.

Using PyQGIS in standalone scripts¶

To start a standalone script, initialize the QGIS resources at the beginning of the script similar to the following code:

from qgis.core import *

# supply path to qgis install location
QgsApplication.setPrefixPath("/path/to/qgis/installation", True)

# create a reference to the QgsApplication, setting the
# second argument to False disables the GUI
qgs = QgsApplication([], False)

# load providers
qgs.initQgis()

# Write your code here to load some layers, use processing algorithms, etc.

# When your script is complete, call exitQgis() to remove the provider and
# layer registries from memory
qgs.exitQgis()

We begin by importing the qgis.core module and then configuring the prefix path. The prefix path is the location where QGIS is installed on your system. It is configured in the script by calling the setPrefixPath method. The second argument of setPrefixPath is set to True, which controls whether the default paths are used.

The QGIS install path varies by platform; the easiest way to find it for your your system is to use the Python Console from within QGIS and look at the output from running QgsApplication.prefixPath().

After the prefix path is configured, we save a reference to QgsApplication in the variable qgs. The second argument is set to False, which indicates that we do not plan to use the GUI since we are writing a standalone script. With the QgsApplication configured, we load the QGIS data providers and layer registry by calling the qgs.initQgis() method. With QGIS initialized, we are ready to write the rest of the script. Finally, we wrap up by calling qgs.exitQgis() to remove the data providers and layer registry from memory.

Using PyQGIS in custom applications¶

The only difference between Using PyQGIS in standalone scripts and a custom PyQGIS application is the second argument when instantiating the QgsApplication. Pass True instead of False to indicate that we plan to use a GUI.

from qgis.core import *

# supply path to qgis install location
QgsApplication.setPrefixPath("/path/to/qgis/installation", True)

# create a reference to the QgsApplication
# setting the second argument to True enables the GUI, which we need to do
# since this is a custom application
qgs = QgsApplication([], True)

# load providers
qgs.initQgis()

# Write your code here to load some layers, use processing algorithms, etc.

# When your script is complete, call exitQgis() to remove the provider and
# layer registries from memory
qgs.exitQgis()

Now you can work with QGIS API — load layers and do some processing or fire up a GUI with a map canvas. The possibilities are endless :-)

사용자 정의 응용 프로그램 실행¶

QGIS 라이브러리 및 적절한 파이썬 모듈을 기본 위치에서 찾을 수 없을 경우 사용자 시스템의 어디에서 탐색해야 하는지 설정해줘야 합니다. 그렇지 않으면 파이썬이 오류 메시지를 표출할 것입니다.

>>> import qgis.core
ImportError: No module named qgis.core

This can be fixed by setting the PYTHONPATH environment variable. In the following commands, qgispath should be replaced with your actual QGIS installation path:

• on Linux: export PYTHONPATH=/qgispath/share/qgis/python
• on Windows: set PYTHONPATH=c:\qgispath\python

The path to the PyQGIS modules is now known, however they depend on qgis_core and qgis_gui libraries (the Python modules serve only as wrappers). Path to these libraries is typically unknown for the operating system, so you get an import error again (the message might vary depending on the system):

>>> import qgis.core
ImportError: libqgis_core.so.1.5.0: cannot open shared object file: No such file or directory

이 문제를 해결하려면 QGIS 라이브러리가 있는 디렉터리를 동적 링커의 탐색 경로에 추가하십시오.

• on Linux: export LD_LIBRARY_PATH=/qgispath/lib
• on Windows: set PATH=C:\qgispath;%PATH%

이러한 명령어를 시동과정을 처리하는 부트스트랩 스크립트에 넣어 둘 수 있습니다. PyQGIS를 이용하는 사용자 정의 응용 프로그램을 배포할 경우 보통 다음 두 가지 방법을 쓸 수 있습니다.

• require user to install QGIS on his platform prior to installing your application. The application installer should look for default locations of QGIS libraries and allow user to set the path if not found. This approach has the advantage of being simpler, however it requires user to do more steps.

• QGIS를 응용 프로그램과 함께 패키지하는 방법입니다. 응용 프로그램을 배포하는 데 더 많은 노력이 필요하고 용량이 더 커지게 되지만, 사용자가 추가로 다른 소프트웨어를 다운로드해 설치해야 하는 부담이 줄어들게 됩니다.

The two deployment models can be mixed - deploy standalone application on Windows and macOS, for Linux leave the installation of QGIS up to user and his package manager.