[QGIS-Developer] Detect a Map Canvas Mouse Event

[Jacky Volpes]

Hello,

Here is a snipped of code that can help you.
To test this you have to:
- Show python console
- enable the polygonal digitizing tool (must be the active tool before 
launching this snippet)
- execute the code in the python editor
- start digitizing
- see the area printing in the console

Don't hesitate if you have further questions.

Regards,
Jacky Volpes - Djedouas - Oslandia

---

# Measurement object (adapt with crs/transform context/ellipsoid)
da = QgsDistanceArea()
da.setSourceCrs(QgsProject.instance().crs(), 
QgsProject.instance().transformContext())
# If distance measurement must use ellipsoid
da.setEllipsoid(QgsProject.instance().ellipsoid())

# This is a demonstration function to adapt with your needs
def showArea(current_point):
     if not isinstance(iface.mapCanvas().mapTool(), 
QgsMapToolDigitizeFeature):
         return

     # Snapping
     snapped_point = 
iface.mapCanvas().snappingUtils().snapToMap(current_point).point()
     if not snapped_point.isEmpty():
         current_point = snapped_point

     # Coordinates in map coordinates
     points = [QgsPointXY(point) for point in 
iface.mapCanvas().mapTool().pointsZM()]
     points.append(current_point)

     # Show area
     print(da.measurePolygon(points))

# Must be handled correctly in the final code, but here is for testing
iface.mapCanvas().xyCoordinates.connect(showArea)








Le 05/04/2023 à 17:56, Catania, Luke A ERDC-RDE-GRL-VA CIV via 
QGIS-Developer a écrit :
>
> Looking for something like
>
> canvas.xyCoordinates.connect( self.canvasMoveEvent )
>
> but that’s from a 7 year old post so looks like xyCoordinates is not 
> in QGIS 3.x
>
> *From:* QGIS-Developer <qgis-developer-bounces at lists.osgeo.org> *On 
> Behalf Of *Catania, Luke A ERDC-RDE-GRL-VA CIV via QGIS-Developer
> *Sent:* Wednesday, April 5, 2023 11:53 AM
> *To:* qgis-developer at lists.osgeo.org
> *Subject:* Re: [QGIS-Developer] Detect a Map Canvas Mouse Event
>
> I found
>
> QgsMapToolEmitPoint, QgsMapTooland |canvas.setMapTool(…)|
> ||
>
> |So I declared my class as |AoiSizeValidator(QgsMapToolEmitPoint)
>
> ||
> |But gave that a try and it gets me x,y, initially but when I select 
> an add layer from the qgis edit menu, I guess it sets a new map tool 
> so mine gets overridden.  So looks like I need a different approach to 
> get xy from the map canvas. |
>
> *From:* QGIS-Developer <qgis-developer-bounces at lists.osgeo.org> *On 
> Behalf Of *Catania, Luke A ERDC-RDE-GRL-VA CIV via QGIS-Developer
> *Sent:* Wednesday, April 5, 2023 11:27 AM
> *To:* qgis-developer at lists.osgeo.org
> *Subject:* [QGIS-Developer] Detect a Map Canvas Mouse Event
>
> Trying to get a map canvas event when canvas is clicked and mouse is 
> dragged.  I have code that creates an empty layer, but I use the QGIS 
> edit menu to add the actually layer.  I want to be able to track the 
> mouse movement so I can calculated the area of the feature being drawn 
> in real time so I can make sure the area is within a defined range.
>
> Is there an event I can connect to so I can run my custom code when 
> the even occurs?
>
>
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-- 
Jacky Volpes

Ingénieur SIG - Oslandia
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