Draw a Line between two points and zoom on the new layer - PyQGIS

Question

In my QGIS3 Plug-in I have this code to draw a line between two points. The code works, but after running it, QGIS zooms somewhere in the middle of Pacific Ocean, when I'd like to zoom on the new layer ("line"). The problem occurs at the last line of this code when I call addMapLayers().

def drawLine(self, line_start, line_end):
  start_point = QgsPoint(line_start.asPoint())
  end_point = QgsPoint(line_end.asPoint())        
  v_layer = QgsVectorLayer("LineString", "line", "memory")
  pr = v_layer.dataProvider()
  seg = QgsFeature()
  seg.setGeometry(QgsGeometry.fromPolyline([start_point, end_point]))
  pr.addFeatures( [ seg ] )
  v_layer.updateExtents()
  crs = v_layer.crs()
  crs.createFromId(4326)
  v_layer.setCrs(crs)
  QgsProject.instance().addMapLayers([v_layer])

I tried to add iface.zoomToActiveLayer() but nothing changed. How can I zoom on this new layer avoiding the Pacific Ocean issue?

Answer 1

Try specifying the CRS when you construct your QgsVectorLayer object e.g.

v_layer = QgsVectorLayer('LineString?crs=epsg:4326', 'line', 'memory')

Unfortunately, you don't show us what objects you are passing to your drawLine() function as the line_start and line_end arguments, however running the code below which directly creates QgsPoint() objects for the start_point and end_point works fine in the Python console in QGIS 3.4.

start_point = QgsPoint(135.0, -15.0)
end_point = QgsPoint(137.5, -16.5)
v_layer = QgsVectorLayer('LineString?crs=epsg:4326', 'line', 'memory')
pr = v_layer.dataProvider()
seg = QgsFeature()
seg.setGeometry(QgsGeometry.fromPolyline([start_point, end_point]))
pr.addFeatures([ seg ])
QgsProject.instance().addMapLayers([v_layer])
iface.zoomToActiveLayer()