Can you write standalone Python scripts in QGIS?

Can you write standalone Python scripts in QGIS?

One can write standalone pyqgis scripts that can be run via the Python Console in QGIS. With a few tweaks, you can make your standalone scripts run via the Processing Framework. This has several advantages.

Which is the runalg method in QGIS API?

To do so, you can use QGIS API commands, or, even easier, use one of the handy methods provided for such tasks. The runalg method returns a dictionary with the output names (the ones shown in the algorithm description) as keys and the file paths of those outputs as values.

Is there a way to automate tasks in QGIS?

You can automate a lot of tasks in QGIS using Python scripting (PyQGIS) and the Processing Framework. Most of the time, you would run these scripts manually while QGIS is open. While that is helpful, many times you need a way to run this jobs via the command-line and without needing to open QGIS.

How to schedule tasks in the QGIS scheduler?

Launch the Task Scheduler and click Create Basic Task. Linux and Mac users can use cron jobs to schedule tasks. Name the task as Daily Download and Cleanup and click Next. Select a time as per your liking and click Next. Choose Start a program as the Action and click Next. Click Browse and locate the launch.bat script. Click Next.

How to create a processing layer in QGIS?

For convenience, you may directly download a geopackage containing the above layer from below: In the QGIS Browser Panel, locate the directory where you saved your downloaded data. Expand the zip or the gpkg entry and select the ne_10m_admin_0_countries layer. Drag the layer to the canvas. Go to Processing ‣ Toolbox.

Which is the best class to use in qgis3?

QGIS3 has a new class called QgsFeatureSink which is the preferred way to create objects that can accept new features. The output needs only 2 fields – one for the value of dissolved field and another for the sum of the selected field.

How to dissolve with sum in qgis3 script?

In the Dissolve with Sum dialog, select the ne_10m_admin_0_countries as the Input layer. This time, make sure you check the Selected features only box. Choose SUBREGION as the Dissolve field and POP_EST as the Sum field. Once the processing finishes, click Close and switch back to the main QGIS window.

One can write standalone pyqgis scripts that can be run via the Python Console in QGIS. With a few tweaks, you can make your standalone scripts run via the Processing Framework. This has several advantages. First, taking user input and writing output files is far easier because Processing Framework offers standardized user interface for these.

How to update plugin from QGIS 2 to QGIS 3?

Running the 2to3 script again looked ok, with a number of changes required. These changes can be applied with –w flag: For the next step I booted up my favourite IDE PyCharm. I created a bat file that launched PyCharm with the QGIS dev environmental variables.

What’s the difference between QGIS 2 and 3?

It seems QGIS 3 deals with the icon slightly differently. icon_rc.py is no longer needed, and it seems was not used on my other plugin either. I still had some errors.

How does a custom function in QGIS work?

We will define a custom function named GetUtmZone that will calculate the UTM zone number for each feature. Since custom functions in QGIS work at the feature level. We will use the centroid of the feature’s geometry and compute the UTM Zone from the latitude and longitude of the centroid geometry.

How to use the map tip tool in QGIS?

One of the hidden gems in QGIS is the Map Tip tool. This tool shows user-defined text when you hover over a feature. Right-click the ne_10m_populated_places_simple layer and select Properties. Switch to the Display tab. Here you can enter any text that will be displayed when you hover over the features of the layer.

How to make a pyqgis script with osgeo4w?

An essential first step is to ensure that all environment variables are set correctly. The most reliable approach is to go to C:\\OSGeo4W64\\bin (or wherever OSGeo4W is installed on your machine), make a copy of qgis-dev-g7.bat (or any other QGIS version that you have installed) and rename it to pycharm.bat:

How to ask your own question in pyqgis?

Asking for help, clarification, or responding to other answers. Making statements based on opinion; back them up with references or personal experience. To learn more, see our tips on writing great answers. Not the answer you’re looking for? Browse other questions tagged qgis pyqgis qgis-processing or ask your own question.

How to write new processing algorithms in QGIS?

Within QGIS, you can use Create new script in the Scripts menu at the top of the Processing Toolbox to open the Processing Script Editor where you can write your code. To simplify the task, you can start with a script template by using Create new script from template from the same menu.

How to run dissolve with sum script in QGIS?

Right-click the dissolve_with_sum script and select Execute. Select the inputs as before and click Run. A new output layer will be added to QGIS. This will contain dissolved geometries only from the selected features in the input layer. You will also note that the output layer will contain only 2 fields as expected.

How to dissolve geometries in a QGIS script?

You will see the selected features highlighted in yellow. Right-click the dissolve_with_sum script and select Execute. Select the inputs as before and click Run. A new output layer will be added to QGIS. This will contain dissolved geometries only from the selected features in the input layer.

How to create a Processing Toolbox in QGIS?

In the QGIS Browser Panel, locate the directory where you saved your downloaded data. Expand the zip or the gpkg entry and select the ne_10m_admin_0_countries layer. Drag the layer to the canvas. Go to Processing ‣ Toolbox.

What causes QGIS-python.exe to stop working?

In technical terms, it seems that you now need to instantiate the QApplication object before making the call to QgsApplication.initQgis () — the example program in the book instantiates the QApplication object after calling QgsApplication.initQgis (), which causes the program to crash.

How to prevent Python script from crashing Stack Overflow?

They all do the same massive disservice: silently and invisibly hiding error conditions that can otherwise be quickly detected and dispatched.” For small scripts this should be sufficient, for larger scripts, I’d recommend using pythons built-in logging, which offers a lot more power for very little extra work.

Why do algorithms run in a separate thread in QGIS?

By default, Processing runs algorithms in a separate thread in order to keep QGIS responsive while the processing task runs. If your algorithm is regularly crashing, you are probably using API calls which are not safe to do in a background thread.

How to create a processing script in Python?

Expand the Scripts group in the Processing Toolbox and select Create a new script. For a python script to be recognized as a Processing script, the beginning of the script must be the specifications of the input and outputs. This will be used to construct the user interface to run the script.

What can you do with QGIS as a beginner?

QGIS has a powerful programming interface that allows you to extend the core functionality of the software as well as write scripts to automate your tasks. QGIS supports the popular Python scripting language. Even if you are a beginner, learning a little bit of Python and QGIS programming interface…

How to access the current active layer in QGIS?

For interacting with the QGIS environment, we must use the iface variable. To access the currently active layer in QGIS, you can type the following and press Enter. This command fetches the reference to the currently loaded layer and stores it in the layer variable.

Which is the best way to use pyqgis?

It should ideally be handled in a slot that is connected to lastWindowClosed () signal of the application. Consulting the PyQGis documentation, you’ll find that there are four main ways to utilize the PyQGis API: outside QGIS (in the Python shell or creating an applications with PyQt4 and not Tkinter (why import Tkinter twice ?)

What’s the difference between QGIS and standalone applications?

This leads me to believe that the difference is that the QGIS application correctly sets external environment variables, but those variables are not set properly when I run it as a standalone script.

How to add a vector layer in QGIS?

This QGIS Python Tutorial series will discuss about how to get features of a vector layer, add or delete a field and updating attribute value. I think this tutorial is quite interesting because in the previous post already discussed how to add a vector layer into QGIS map canvas.

When does a feature change in QGIS plugin?

When the user creates a new feature, the plugin should: The modifications do not need any user input, and can happen in ‘real-time’ or following a commitChanges (), but the user should remain in (or be returned to) an editing session. What is the best strategy for this?

How to add a field in QGIS Python?

After that using addAttributes method then a field is added using QgsField class with taken two parameters: Field Name and Type. For field’s type can be defined using QVariant.

How to create a processing script in QGIS?

go to Processing > Toolbox ; from the Processing toolbox (just activated on the right side of the main QGIS window), go to Create new script menu under the Tools group in the Scripts algorithms block of the toolbox; to be recognized as a Processing script, it is necessary to specify the inputs and the outputs.

What kind of programming language does QGIS support?

QGIS supports the popular Python scripting language. Even if you are a beginner, learning a little bit of Python and QGIS programming interface will allow you to be much more productive in your work. This tutorial assumes no prior programming knowledge and is intended to give an introduction to python scripting in QGIS (PyQGIS).

How to turn layers and tables into QGIS objects?

Layers and tables values are strings containing the filepath of the corresponding object. To turn them into a QGIS object, you can use the processing.getObjectFromUri () function. Multiple inputs also have a string value, which contains the filepaths to all selected objects, separated by semicolons (; ).

How to turn multiple inputs into a QGIS object?

To turn them into a QGIS object, you can use the processing.getObjectFromUri () function. Multiple inputs also have a string value, which contains the filepaths to all selected objects, separated by semicolons (; ). Outputs are defined in a similar manner, using the following tags:

What do you do with the map canvas in QGIS?

The QgsMapCanvas class also controls refreshing of the rendered map. Besides this item which acts as a background, there may be more map canvas items. Typical map canvas items are rubber bands (used for measuring, vector editing etc.) or vertex markers.

Which is the most important widget in QGIS?

The Map canvas widget is probably the most important widget within QGIS because it shows the map composed from overlaid map layers and allows interaction with the map and layers. The canvas always shows a part of the map defined by the current canvas extent.

What can you do with a map canvas?

Typical map canvas items are rubber bands (used for measuring, vector editing etc.) or vertex markers. The canvas items are usually used to give visual feedback for map tools, for example, when creating a new polygon, the map tool creates a rubber band canvas item that shows the current shape of the polygon.

How to customize the QGIS interface in Python?

We will also explore GUI programming techniques for customizing the QGIS interface using Qt widgets. This course requires basic knowledge of Python. If you are not familiar with Python, it is strongly recommended you complete our Python Foundation for Spatial Analysis course. We will build upon the exercises covered in that course.

What can you do with pyqgis in Python?

QGIS provides a Python API (Application Programming Interface), commonly known as PyQGIS. The API is vast and very capable. Almost every operation that you can do using QGIS – can be done using the API. This allows developers to write code to build new tools, customize the interface and automate workflows.

Which is the most powerful tool in QGIS?

One of the most powerful QGIS tools is the possibility to create custom Python codes and then adding them to the Processing Toolbox. This operation has several advantages, for example: the integration of the custom script within the QGIS Graphical Modeler for managing particular situations not covered by the default tools.

Is there a processing console in QGIS for Python?

Models involving several algorithms can be defined using the command-line interface, and additional operations such as loops and conditional sentences can be added to create more flexible and powerful workflows. There is not a processing console in QGIS, but all processing commands are available instead from the QGIS built-in Python console .

How to make a QGIS app for rendering layers?

I made a simple standalone QGIS app for rendering a set of layers and export it as a PDF file. When i use iface.mapCanvas ().mapRenderer () (inside QGIS console) for rendering, my output is OK.