RoadNetwork

Road network

Each road

• has an identification e.g. D907
• is composed by a series of ordered edges (simple linestrings)

Markers are positioned along the roads e.g. Their position is often measured with a GPS (X,Y)

RoadNetwork

Topology

The road network is a GRAPH built with edges and nodes

• each edge has
  a start and end node
• an edge can have
  • a previous edge
  • a next edge
• intersecting edges are cut by a node (if they are on the same level)

RoadNetwork

Position & references

This simple organization of roads, edges and markers allows to determine a position of any object based on:

• a road code: D902
• a marker code: 1
• an abscissa: 500m

You can also provide an optional
offset: 3m and side: left

Any point within a distance of 50m of any road will have its references: D902 PR 1 + 500m (3m left)

RoadNetwork

Linear referencing

Each data object, point or (multi)linestring, is defined by its references calculated from the road network:

• Points: trees, street lights, car accidents, etc.
• Linestrings: paintings, safety barriers, roadworks, etc.

We must be able to:

• calculate the references from the object geometry
• create a geometry based on given references
  • a point
  • a multi-linestring between 2 references

RoadNetwork

Corner cases

Discontinuity: edges could have been deleted (or have changed status)

Roundabouts have their own road code GIR D35-D80 and cut the other roads

RoadNetwork

Data model

All the logic is stored inside a PostgreSQL database

A simple set of tables: roads, edges, nodes, markers, glossary, managed_objects + views

Many functions to calculate references, geometries, among:
get_road_point_from_reference
get_road_substring_from_references
update_table_references_from_geometries
update_table_geometry_from_references

Trigger functions in charge of maintaining the road network topology (automatic node creation, split intersected edges, etc.)

RoadNetwork

Context

Funded by the Département du Calvados (French department)

Objectives

• They needed to get rid of a proprietary software & use only FOSS4G tools
• The data must be stored in a PostgreSQL database
• Visualization & Editing must be done inside QGIS , with the help of a plugin
• Calculations (references, geometry editing) must be made available for Lizmap Web Client

RoadNetwork

Administration tools

Processing algorithms which allow to:

• Create the database structure with all the tables/functions, etc.
• Upgrade the structure (if upgrading your plugin)
• Create a QGIS administration project with all the layers, styles, labels, actions, etc.
• Import data from template edges and markers tables

RoadNetwork

QGIS administration project

RoadNetwork

Tools - Quick search (CTRL+K)

RoadNetwork

Tools - Get references on map click (hover supported)

RoadNetwork

Editing rules

Data are not edited in the production schema road_graph but in a dedicated editing sessions schema

• The user creates a polygon and clones an extract of the production data in a sanbox
• Editing is made with QGIS tools: forms, topology
• QGIS automatic transaction grouping has been activated in the project: changes made with triggers are visible live
• A map tool helps to create roundabouts
• Modifications are then merged back into the road_graph schema

RoadNetwork

Managed objects

The local authorities manages a lot of data based on the road network : roadworks, asphalt rehabilitation, road signs, hedge pruning.

The managed_objects layer lists all the PostgreSQL tables impacted by any graph modification

When the user merges the data from the editing session, every impacted object is
automatically updated based on the rule chosen by the admin user.

• Point objects are often not moved but their references must be updated Ex: a road sign
• (Multi)Linestring objects must often follow the changes, but we keep the start & point and only edit the nodes between. Ex: a painting roadwork

RoadNetwork

Conclusion

The QGIS plugin is here to

• create/ugprade the database structure
• visualize the road network
• position with references & get references from position
• edit data safely in a sandbox and use algorithm to copy/merge the data
• import data

The main business logic really lies inside the PostgreSQL database

• schemas and tables, functions, triggers