Routing with several stops using QGIS

Question

I have point layer and a network (segments) stored in a GeoPackage and using QGIS. The number of points and their ids are always different.

What I need is to get a route from first to last points but through several stops in a specific order.

I am thinking in a script or algorithm where to select an order column and then do the shortest path between first and last points setting the rest of it as stops ordered and get a single layer with the entire path.

I've tried the Analysis tools of QGIS and plugins but I can't find a tool with this functionality.

I have also tried the v.net.salesman that computes a route through all the points but it isn't what I need, It can't assign an order to the stops and the route should not be cycle.

Is there any way, using QGIS or PyQGIS, to do that?

Answer 1

The solution requires some basic usage of PyQGIS. This code computes paths for every subsequent pair of points using the order specified in the "order" field. Then all the paths are merged into a single layer.

Add an order column, change your input variables and run this as a script in QGIS 3.

###input###
networkLayerName = 'prg_ulice'
pointLayerName = 'pkt_adresowe'
orderColumnName = 'order'
output = '/home/lpowalka/Documents/dane/geopackage/path.gpkg'
###input###

networkLayer = QgsProject.instance().mapLayersByName(networkLayerName)[0]
pointLayer = QgsProject.instance().mapLayersByName(pointLayerName)[0]

expr = '"{column}" is not null'.format(column=orderColumnName)
pointLayer.selectByExpression(expr)

stops = []
for feat in pointLayer.selectedFeatures():
    stops.append((feat['order'], feat.geometry().asPoint()))

#sort by order column
stops.sort(key=lambda x: x[0])
paths = []
for i, (order, point) in enumerate(stops[0:-1]):
    endPoint = stops[i + 1][1]
    print('Order: ', order)
    print('From {} to {} \n'.format(point, endPoint))
    parameters = {'INPUT': networkLayer,
                'STRATEGY': 0,
                'DIRECTION_FIELD': '',
                'VALUE_FORWARD': '',
                'VALUE_BACKWARD': '',
                'VALUE_BOTH': '',
                'DEFAULT_DIRECTION': 2,
                'SPEED_FIELD': '',
                'DEFAULT_SPEED': 50.0,
                'TOLERANCE': 20.0,
                'START_POINT': point,
                'END_POINT': endPoint,
                'OUTPUT': 'memory:'}


    path = processing.run('qgis:shortestpathpointtopoint', parameters)['OUTPUT']
    paths.append(path)

params = {'LAYERS': paths, 'OUTPUT': output}
pathsMerged = processing.run('qgis:mergevectorlayers', params)['OUTPUT']
vlayer = QgsVectorLayer(pathsMerged, 'result', 'ogr')
QgsProject.instance().addMapLayer(vlayer)