[GIS] Automatically refreshing mapCanvas

qgisqgis-3qgis-plugins

Is it possible to automatically refresh the QGIS map canvas in the background?

I have a .geojson file with the data. This data changes (in case of a simulation) but the map canvas only refreshes after I press the F5 button (refresh). In my case it should refresh the map every 100msec.

In the "layer properties/Rendering" there is a option "Refresh layer at interval (seconds)". I activated this but it has not the function I've searched for.

I found the command for the Python Console: iface.mapCanvas().refreshAllLayers().
This is exactly the function I've searched for. But I need it called periodically in the background.
I tried this with a self-written plugin, but without success. (Python script with an endless loop -> GUI freezes)

Best Answer

Go to: Settings menu > Options > Rendering tab > Change map update interval to 100 ms

If this doesn't work, make a bug report at https://issues.qgis.org.

Related Solutions

[GIS] Does mapCanvas().refresh() not work in QGIS 2.6

It may very well be a bug as I also cannot get the canvas to refresh. You can try the following as a workaround:

myLayer.triggerRepaint()

To refresh all layers following function can be used:

def refresh_layers(self):
    for layer in qgis.utils.iface.mapCanvas().layers():
        layer.triggerRepaint()

Custom map pan tool freezes map canvas extent, cuts off map tiles (QGIS 3.18)

First of all, why do you expect that the canvas extent should change using your code? I don't see a new assignment to map canvas extent or map canvas center anywhere in your code. Therefore the canvas basically stays the same and appears frozen.

QgsMapToolPan updates the position and extent in the canvasReleaseEvent function, which you are hiding with your custom behaviour in Pan::canvasReleaseEvent (doing nothing but setting the cursor!).

So your options would be to either call the base implementation using something like

void Pan::canvasReleaseEvent(QgsMapMouseEvent *e)
{
    QgsMapToolPan::canvasReleaseEvent(e)
    setCursor(Qt::OpenHandCursor);
}

or if you don't want to call the default implementation an option would be to use panActionEnd, which ends the pan action and redraws the canvas.

void Pan::canvasReleaseEvent(QgsMapMouseEvent *e)
{
    setCursor(Qt::OpenHandCursor);
    mCanvas->panActionEnd(e->pos());
}

Or exactly the same using python:

class Pan(QgsMapToolPan):
    def __init__(self, canvas):
        super().__init__(canvas)
        self.canvas = canvas
        
    def canvasPressEvent(self, e):
        self.setCursor(Qt.ClosedHandCursor)
        
    def canvasReleaseEvent(self, e):
        self.setCursor(Qt.OpenHandCursor)
        self.canvas.panActionEnd(e.pos())

tool = Pan(iface.mapCanvas())
iface.mapCanvas().setMapTool(tool)

Best Answer

Related Solutions

[GIS] Does mapCanvas().refresh() not work in QGIS 2.6

Custom map pan tool freezes map canvas extent, cuts off map tiles (QGIS 3.18)

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