Performing a Best Route Analysis
Concept Procedure Quick Reference
 
 
 

Using a network topology, which is made up of drawing objects and their relationship data, you can calculate the best route from a starting point in the drawing, to one or more visit points, and back to the starting point. AutoCAD Map 3D determines the optimal route based on values of direction and resistance. For example, in a street network, you can find the best route to travel when visiting several customer sites from your hotel.

If a path has a total resistance lower than the Minimum Resistance value, the path is ignored. Similarly, if a path has a total resistance greater than the Maximum Resistance value, the path is ignored.

Using SQL Data in Expressions

If you specify an expression that uses SQL data, the Link Template list includes only link templates defined in the drawing where the topology is loaded — in the source drawing, if you loaded the topology from source drawings; in the current drawing, if you loaded the topology from the current drawing. Also, be sure that the appropriate data source is attached and connected in the current drawing.

Travel Time in Network Topologies

To carry out a best route analysis on a road network based on time rather than distance, assign a speed or speed limit to each link using an object data field or a field in a linked external database. You then set the Link Direct Resistance property to an expression that uses this speed limit data, for example:

(/ .length (* :speed@street_data 5280))

which divides the length of each link by the average speed per foot (where 5280 is the number of feet in a mile).

The resulting analysis shows the best route, in terms of time, not distance.

Object Data Stored for a Best Route Topology

If you save the results of a best route analysis to a new topology, AutoCAD Map 3D adds topology information, stored as object data, on each element that makes up the best route topology. The object data table contains information about the order of the links visited and the resistance used to calculate the best route. The object data table added is like the one shown in the following table.

Topology Name Object Data Table Object Data Field
SAMPLE BR_SAMPLE Path Link Visit Order
    Evaluated Link Forward Resistance
    Evaluated Link Reverse Resistance
    Evaluated Start Node Resistance
    Evaluated End Node Resistance
    Evaluated Link Direction

Displaying Visit Order Using Annotation

To display the order in which to visit points, you use AutoCAD Map 3D's annotation feature to label the best route with the object data described above.

Editing a Best Route Topology

If you change the direction or resistance of an object in a best route topology, the best route shown may no longer be the optimal route, and you should recalculate the best route. For example, if you change the direction of a link from bi-directional to forward or reverse, it may change the best route.

NoteThe best route cannot be calculated if the network topology contains negative resistance values or if all resistance values equal "0" (or use expressions that evaluate to zero). In layman's terms, if all resistance values equal zero, every possible route is as good as any other route, and there is no "best" route to travel.
See Also