Network Objects: road networks, pipelines, canals

Several modules of ESS systems like AirWare, RiskWare, or WaterWare use networks of line features such as street networks, river networks, or pipelines as input data.

As an example, the traffic emission/immission module in AirWare requires a road network and associated traffic frequency or emission data. The road network and attribute data can be imported from an appropriate ArcInfo coverage.

Alternatively, a simple ASCII data format can be used; two sets of data are required:

node data supplying the geometry
arc data supplying the attributes of the line segments.

. The set of attributes depends on the kind of line type (road, rail, canal, river, pipeline), and the methods (models) that will use these data. The attributes refer to Descriptors defined in the expert system.

The basic format of these data, combined in a single file is simple: nodes are simply defined by an ID and an x and y coordinate in standard map (world) coordinates:

NETWORK
network_name
ME1               # metadata records 
ME2
ME3
TABLE 
nodes
E node_ID
E x_coordinate
E y_coordinate
D 0001  12300.50  825.00
D 0001  12320.00  826.00
D 0003  12300.00  800.00
END_TABLE
TABLE 
arcs
E  ID
E  FROM_node
E  TO_node
E  segment_name
E  road_type
E  car_frequency
E  No_of_lanes
D  1 001 002 Main_street main_road 2000.0 4
D  2 002 003 Main_street main_road 2020.0 4
D  3 003 004 Main_street main_road 2100.0 4
.....
ENDTABLE
ENDNETWORK

An alternative syntax supports the import of the data from external files instead of embedding the data into the object template itself:

NETWORK
network_name      # max. 30 characters
ME1               # metadata records
ME2
ME3
TABLE
nodes
E node_ID
E x_coordinate
E y_coordinate
R /data/import/nodefile1.dat
END_TABLE
TABLE
arcs
E ID
E FROM_node     # integer ID
E TO_node       # integer ID
E segment_name  # max 30 characters
E road_type     # character
E car_frequency # defined in the corresponding Descriptor
E No_of_lanes
R /data/import/arcfile1.dat
ENDTABLE
ENDNETWORK

Here the data records D are replaced by a reference R that can either be a filename, or potentially also a URL or database query string (SQL).

Please note that the arc ID should start at 1, and be organized consecutively. ID and FROM and TO node, as well as at least one attribute are mandatory.

The same segment denoted by segment_name can consist of several individual arcs;

The list of attributes of a road segment is open, i.e., an arbitrary number of attributes can be used. Examples could be Average Speed, Number of Lanes, Segment length, Traffic capacity, Speed limit, etc. The attributes, however, have to be defined as Descriptors in the systems knowledge base to allow their editing, and the display of the network with the attribute data supplying either color or width information.

An example of a descriptor definition (from the file: ./data/KB/Descriptors for a road segment attribute would be:

DESCRIPTOR
street_width
A StreetWidth
T S
U m
V very_narrow [ 5, 6, 7]
V narrow      [ 7, 8, 9]
V average     [ 9,10,15]
V wide        [15,20,30]
V very_wide   [30,40,60]
R 3000 / 3001 /3002 /3003 /
Q What is the average width in meter for this road segment ?
LAYOUT
FORMAT %2.0f
ENDLAYOUT
ENDDESCRIPTOR