According to a specific aggregation design, this algorithm aims to generate a set of Origin-Destination (OD) matrices based on individual mobility flow information. First, it spatially aggregates individual mobility flows within a defined study area, which is divided into multiple spatial units. Then, it computes an optimized OD matrix that minimizes travel distance while preserving the total number of people entering and exiting each spatial unit (i.e., the marginals). Additionally, it generates a random OD matrix in which flows are assigned randomly while still preserving the marginals.
The input table contains individual mobility flow information from an origin to a destination (journey to work for example). Every origin and destination is represented by a point. The input table is a 6 columns csv file with column names, the value separator is a semicolon ",". Each row of the file represents an individual.
- ID: Identifier of the individual
- X_Ori: X coordinate of the Origin (projected in meters)
- Y_Ori: Y coordinate of the Origin (projected in meters)
- X_Des: X coordinate of the Destination (projected in meters)
- Y_Des: Y coordinate of the Destination (projected in meters)
- Weight: Statistical weight of the individual
An example is provided in the csv file country containing mobility information on 10,000 fake individuals. In this case the coordinated are projected in epsg 3035. It is important to work with coordinates in meters and to be aware of the epsg code of the projection.
The script importTable.R imports the input table in a PostGIS database. The imported table contains 4 columns: one id, a weight and two geometries orig and dest. Note that a PostGIS database should be created before in order to get the following information needed to run the script:
- host: Server host
- port: Port of the server host
- db: Database
- user: User name
- mdp: Password
Once the table is imported into a PostGIS database, an aggregation design can be set up in the script main.R with the following information:
- city: Name of the study area
- xcenter: X center of the study area
- ycenter: Y center of the study area
- shape: Shape of the study area (square & circle)
- radius: Half side length of the shape (need to be a multiple of scale)
- scale: Side length of the grid cell
The script main.R runs the function XS.R which returns a list containing 5 elements based on the aggregation design.
- idsim: Simulation ID
- matflows: OD matrix
- matcost: Cost associated with the OD matrix
- matmin: Optimized OD matrix
- matrand: Randomized OD matrix
- shp: Associated spatial object (grid cells)
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