I have a aggregate process that takes about 9h to run collecting data from a point dataset to put into a line.
The process is
aggregate(layer:='Roads_10m_Chainage.tab', aggregate:='max', expression:="distance" * (attribute(@parent, 'RoadMntnc') = attribute($currentfeature, 'RoadMntnc')),filter:= within(start_point(geometry(@parent)),buffer($geometry,5,10)))
This ensures the value from the point data has the same RoadMntnc value as the line it's looking at the start point of. The buffer ensures it collects the closest value -this works as the chainage is 10m so there will always be a point within 5m.
I was hoping to speed up the process by using a PyQGIS selection of the road line and chainage point datasets having the same RoadMntnc value rather than it crunching through the whole dataset.
So far I have
from operator import itemgetter
def Update_Field(fieldName, ntext): # Function to simplify updating fields
print (ntext)
fieldIndex = layer.fields().indexFromName(fieldName)
dpr.changeAttributeValues({feature.id(): {fieldIndex: ntext}})
layer.commitChanges()
roadlist=[]
layer = iface.activeLayer()
dpr = layer.dataProvider()
chainage_layer=QgsVectorLayer(r'Z:\My Drive\Mangoesmapping\Spatial Projects\2019\DSC\126_Road_Updates\Working\Output\DSC_Roads_10m_Chainage.tab', "Chainage", "ogr")
#for feature in layer.getFeatures(): # Create list of unique roads to work through
#if feature['RoadMntnc'] not in roadlist:
# roadlist.append(feature['RoadMntnc'])
roadlist=['Kingston_Rd'] #Manual road list for testing
for road in roadlist: # for each road get key attributes and sort
print (road)
layer.selectByExpression('"RoadMntnc"= \'{0}\''.format(road), QgsVectorLayer.SetSelection)
selection=layer.selectedFeatures()
l_selection=layer.selectedFeatures()
i=1
road_parts=[]
chainage_layer.selectByExpression('"RoadMntnc"= \'{0}\''.format(road), QgsVectorLayer.SetSelection)
chainage_selection=chainage_layer.selectedFeatures()
for f in selection:
for l in chainage_selection:
if f.geometry().intersects(l.geometry()): #how do I check if a 1m buffer of the start point has a chainge point within it?
print (l.id(),l['RoadMntnc'], l['distance'])
#if the above works then update record
#ntext=str(item['Distance'])
#print (ntext)
#fieldName='Start_Chainage'
#Update_Field(fieldName,ntext)
All values are printed in the last line - how to I change the if statement to just show the distance value from the chainage value within 1m of the start of the line?
How do I write the expression to utilize the two selections or modify the aggregate function to use the two selections or use an [envelope][1] to collect the required value?
**UPDATE: Using César Arquero answer**
The buffer to check needs to be around the start point of each road segment. All I need is the chainage feature that intersects this buffer - it should just be one point, but if more than one I need the lowest value.
from operator import itemgetter
def Update_Field(fieldName, ntext): # Function to simplify updating fields
print (ntext)
fieldIndex = layer.fields().indexFromName(fieldName)
dpr.changeAttributeValues({feature.id(): {fieldIndex: ntext}})
layer.commitChanges()
roadlist=[]
layer = QgsProject.instance().mapLayersByName('DSC_Roads')[0]
chainage_layer= QgsProject.instance().mapLayersByName('DSC_Roads_10m_Chainage')[0]
for feature in layer.getFeatures(): # Create list of unique roads to work through
if feature['RoadMntnc'] not in roadlist:
roadlist.append(feature['RoadMntnc'])
#
roadlist=['Dean_Rd'] #for testing
#-----------------------------------------------------------------------
#OPTION 1
for road in roadlist: # for each road get key attributes and sort
i=1
road_parts=[]
request = QgsFeatureRequest(QgsExpression('"RoadMntnc"= \'{0}\''.format(road)))
l_selection = layer.getFeatures(request)
chainage_selection = chainage_layer.getFeatures(request)
for l in l_selection:
geom = l.geometry().asPolyline()
print ("Start: " + str(geom[0]))
print ("End: " + str(geom[-1]))
for c in chainage_selection:
buffer = geom[0].buffer(5,5) #5m buffer with 5 segments
if c.geometry().intersects(buffer):
print(l.id(),c['RoadMntnc'],c['distance'])
#if the above works then update record
# ntext=str(l['distance'])
# print(ntext)
# fieldName='Start_Chainage'
# Update_Field(fieldName,ntext)
**UPDATE 2**
For some reason it's only updating roads that have one section and not multiple and also where there more than one point within the buffer it's not putting in any value. I have cleaned up the code to try and see why it's not functioning as expected...
def Check_Intersection (c_sel, l, start_end): #Find points within start/end of line
geom = l.geometry().asPolyline()
g = QgsGeometry.fromPointXY(geom[start_end])
buffer = g.buffer(10,4) #10m buffer with 4 segments
#buffer_to_iface(buffer) #add buffer to map for testing
for c in c_sel: # for each chainage point -ideally should be envelope in buffer area only
#print (c['RoadMntnc'],c['distance']) #show value for testing
if c.geometry().within(buffer):
print(l.id(),c['RoadMntnc'],int(c['distance']))
#Update record
# layer.startEditing()
# ntext=int(c['distance'])
# fieldName='Start_Chainage2'
# FieldIndex = l.fields().indexFromName(fieldName)
# layer.changeAttributeValue(l.id(), FieldIndex, ntext)
# layer.commitChanges()
break
def buffer_to_iface(buffer): #buffer to iface for testing
buff_layer = QgsVectorLayer('Polygon', 'buffer' , 'memory')
prov = buff_layer.dataProvider()
feat = QgsFeature()
feat.setGeometry(buffer)
prov.addFeatures([feat])
buff_layer.updateExtents()
QgsProject.instance().addMapLayers([buff_layer])[0]
roadlist=[]
layer = QgsProject.instance().mapLayersByName('DSC_Roads')[0]
chainage_layer= QgsProject.instance().mapLayersByName('DSC_Roads_10m_Chainage')[0]
for feature in layer.getFeatures(): # Create list of unique roads to work through
if feature['RoadMntnc'] not in roadlist:
roadlist.append(feature['RoadMntnc'])
#
#roadlist=['Kingston_Rd'] #for testing
#-----------------------------------------------------------------------
for road in roadlist: # for each road select line and point features
request = QgsFeatureRequest(QgsExpression('"RoadMntnc"= \'{0}\''.format(road)))
l_sel = layer.getFeatures(request)
c_sel = chainage_layer.getFeatures(request)
for l in l_sel: # repeat for each road segment
print (str(l.id())+l['RoadMntnc'])
start_end=0 #get start points
Check_Intersection (c_sel,l,start_end)
print ('Completed')
layer.updateFields()
[1]: https://nyalldawson.net/tag/pyqgis/