One of the important tools that AutoCAD Map 3D includes is the capability to work with topologies. It can create and manage them, and more importantly, do analysis from these topologies. Basic training classes, and all of the books I’ve seen, show how to create, manage and perform analysis with topologies. One thing that is absent, is how to take advantage of and access the results after the analysis – it’s the cause of a lot of questions from people I work with.
Before I get on to working with the results, I want to give some background of topologies, and how AutoCAD Map 3D manages them.
Topology is a technique for managing spatial relationships between objects. It is a particularly useful technique for managing networks of objects, such as utilities or streets. The relationships allow you to trace up- or downstream to answer questions, such as:
- What customers will be out of power if this line is down?
- What is the likely source of contaminant (common point upstream) when there are a series of sites that are showing high levels of contaminants?
- What is the shortest route between two locations?
The relationships are created by maintaining unique identifiers for each point or junction and line in data tables. These identifiers are called Primary Keys. The lines will also contain fields to include the identifiers of the points from each end of the line. These are called Foreign Keys. By searching for lines that have a specific point identifier, you can find all the lines that connect to a point, and go from point to associate line to associated point to associated line, etc, much like a monkey swinging from one vine to the next.
Consider the example below. Here is a collection of lines and points. There is graphic representation of the network, and a snapshot of the data tables from the network. Look at point # 2364. It appears to be the end of
that particular network stream. We look for all of the lines that have either a start point or end point value equal to 2364, and we find that line # 6888 has 2364 as an end point. We then look at the other point value and find it is 2359 (the start point and end point allow a topology to show direction as well as just connections), so we search the line table for other lines that have that value. We will find line #’s 6887 and 6921. We can then continue in this process until we get the results we are looking for. For a best route, we will evaluate the potential sets of lines that provide a connection between the two points, and use some criteria to determine the best (usually the shortest lengths) set or route.
AutoCAD Map 3D provides tools and the data structures to create and manage topologies, as well as topology analysis tools. Within the Task-based Workspace, the topology commands can be found on the Object Map ribbon on the Topology panel. The only thing required to create a network topology is a clean network of lines (clean means that the end of one line exactly meets another line – their coordinates should match). Map 3D will create points (called Nodes) at the junction points if they don’t exist in the data.
Once a network topology is created, Map 3D will create Object Data to manage to topological relationships. The nodes will get a table called TPMNODE_topologyname (where topologyname is the name of the topology). You can use the Edit Object Data command (The Object Data panel of the Object Map ribbon) to select a node and review the table information. The ID field is the critical element (the resistance values can be used to manipulate the analysis – for example, the resistance on a point could be a time factor for an average stop at a stop sign so route can be qualitatively compared including stops, turns, etc).
You can also see the values of the object data by selecting an object and reviewing the Properties (on newer versions of map 3D).
The lines (Map 3D calls them LINKS) will get their own set of Object Data, called TPMLINK_topologyname. The line (or link) object data will include additional fields. The critical elements are the Start_Node and End_Node fields, which are how Map 3D manages the topology relationships.
The purpose of creating and managing topology is to perform analysis, and the tools are also available on the Topology panel of the Object Map ribbon. The three network analysis tools are Shortest Path, Best Route and Flood Trace.
When completing the analysis, you have the option of highlighting the results with a color (it will go away with the next redraw), or save to a topology. You will give the results a name (my example attached was a flood trace, and I named the resulting topology FloodResults).
Once the topology is created, I can always re-highlight the topology, but it goes away with each redraw. That makes it a bit difficult to use for further analysis or to even print the results.
The easy way to work with them at this point is to save the drawing with the result topology (or topologies) and open a new drawing. In the new drawing, use the Map 3D drawing attach tools to connect to the results drawing.
In the Map Explorer of the Task Pane, the topologies from the attached drawing will be visible in a greyed out icon. This means the topology hasn’t been loaded into the current drawing.
Right-click on the result topology and select the Load Topology option under the Administration menu.
This will open a dialog box with the option to Create objects when loaded. Selecting this will recreate the topology objects in the current drawing, essentially making a copy of the topology data from the original file.
You may have to Zoom Extents to see the newly created data.
At this point, we now have just the objects and topology from the result topology we created. We can save this and have it available for future applications and uses, such as printing route maps or performing buffers, etc. In addition, the objects will have not only the object data from the results topology, but it will also have the data from the original topology and any object data from the original objects.