How is the map canvas implemented in QGIS?

How is the map canvas implemented in QGIS?

Map canvas is implemented as QgsMapCanvas class in qgis.gui module. The implementation is based on the Qt Graphics View framework. This framework generally provides a surface and a view where custom graphics items are placed and user can interact with them.

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 shows always a part of the map defined by the current canvas extent.

How is the interaction with the map canvas done?

The interaction is done through the use of map tools : there are tools for panning, zooming, identifying layers, measuring, vector editing and others. Similar to other graphics programs, there is always one tool active and the user can switch between the available tools.

How can I embed QGIS in a window?

It can be also embedded into an existing widget or window. When using .ui files and Qt Designer, place a QWidget on the form and promote it to a new class: set QgsMapCanvas as class name and set qgis.gui as header file. The pyuic4 utility will take care of it. This is a very convenient way of embedding the canvas.

https://www.youtube.com/watch?v=QiQZv7S2VFk

How to create dynamic maps in QGIS Python?

This section of the preview chapter, Creating Dynamic Maps from QGIS Python Programming CookBook takes a look at how to control an object through the Map Canvas, change map units, and how to loop through map layers.

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.

How does the canvas interact with the map?

The canvas shows always a part of the map defined by the current canvas extent. The interaction is done through the use of map tools : there are tools for panning, zooming, identifying layers, measuring, vector editing and others.

Is there a way to embed map canvas?

The pyuic4 utility will take care of it. This is a very convenient way of embedding the canvas. The other possibility is to manually write the code to construct map canvas and other widgets (as children of a main window or dialog) and create a layout. By default, map canvas has black background and does not use anti-aliasing.

How is the context scope set in QGIS?

Sets an expression context scope for the map canvas. This scope is injected into the expression context used for rendering the map, and can be used to apply specific variable overrides for expression evaluation for the map canvas render. This method will overwrite the existing expression context scope for the canvas.

How do you define an extent in QGIS?

In this case, the algorithm dialog disappears and you can click and drag on the QGIS canvas to define the desired extent. Once you release the mouse button, the dialog will reappear and the text box will already have the values corresponding to the defined extent.

Where do I find query builder in QGIS?

Open the Query Builder by opening the Layer Properties and going to the General menu. Under Feature subset, click on the [Query Builder] button to open the Query builder. For example, if you have a regions layer with a TYPE_2 field, you could select only regions that are borough in the Provider specific filter expression box of the Query Builder.

How to add a layer to the QGIS layer?

right-click on QGIS toolbar and check Browser Panel to activate it or select it from the menu (or ); a browser tree with your filesystem, databases and web services is displayed; find the layer in the list; right-click on its name and select Add selected layer(s).