Contents
When do you refresh the map canvas in QGIS?
By default, QGIS renders all visible layers whenever the map canvas is refreshed. The events that trigger a refresh of the map canvas include: QGIS allows you to control the rendering process in a number of ways. Scale-dependent rendering allows you to specify the minimum and maximum scales at which a layer will be visible.
How to control the rendering process in QGIS?
QGIS allows you to control the rendering process in a number of ways. Scale-dependent rendering allows you to specify the minimum and maximum scales at which a layer (raster or vector) will be visible. To set scale-dependent rendering, open the Properties dialog by double-clicking on the layer in the legend.
How to control visibility of layers in QGIS?
Manage Visibility: control visibility of layers and preset layers combination. Filter Legend by Map Content: only the layers that are set visible and whose features intersect the current map canvas have their style rendered in the layers panel. Otherwise, a generic NULL symbol is applied to the layer.
What does a map theme do in QGIS?
A map theme is a snapshot of the current map legend that records: the layers set as visible in the Layers panel and for each visible layer: the reference to the style applied to the layer
How does QGIS allow you to control the rendering process?
QGIS allows you to control the rendering process in a number of ways. Scale-dependent rendering allows you to specify the minimum and maximum scales at which a layer will be visible. To set scale-dependent rendering, open the Properties dialog by double-clicking on the layer in the legend.
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 to get dependable refresh on mapcanvas in Python?
With canvas caching in the mix ( python cookbook, note at the end of the ‘Modifying Vector Layers’ section ), I have to do the following to get a dependable refresh after an edit (in my case from within plugin code in QGIS 2.14): That is, I always call triggerRepaint () on all layers and then call the mapCanvas’s refresh () just to be safe.
How to use notify to automatically refresh layers in QGIS?
This was developed by the wizards from Oslandia and is easily added to any existing table in your PostgreSQL database – including PostGIS tables. This feature was added in version 3.0 (see https://qgis.org/en/site/forusers/visualchangelog30/#feature-trigger-layer-refresh-or-layer-actions-from-postgresql-notify-signal ).
How to update the feature count in QGIS?
By default, QGIS does not display any features for a layer until the entire layer has been rendered. To update the display as features are read from the datastore, choose menu option Settings ‣ Options and click on the Rendering tab. Set the feature count to an appropriate value to update the display during rendering.
How to enable a back buffer in QGIS?
Open the QGIS options dialog using Settings ‣ Options, go to the Rendering tab and select or deselect the following checkboxes: Enable back buffer. This provides better graphics performance at the cost of losing the possibility to cancel rendering and incrementally draw features.
How to identify features in the QGIS toolbar?
The Identify tool allows you to interact with the map canvas and get information on features in a pop-up window. To identify features, use View ‣ Identify features or press Ctrl + Shift + I, or click the Identify features icon on the Attributes toolbar. QGIS offers two ways to identify features with the Identify features tool: