I am attempting to test the feasibility of a vehicle navigation solution in ArcGIS: ArcMap using the Network Analyst extension that can calculate the best route to a destination based on fuel economy variables (as oppose to drive times or just the length of journey). Fuel economy values have been calculated based on information collected from peer reviewed literature for average light duty vehicles. The said values have been added to the roadlinks dataset as an impedance value so that each roadlink has a cost associated with its transversal. As the route finder transverses each roadlink, the impedance values accumulate which results in a total �??cost�?? for the journey.
To verify and assess the accuracy of the solution, routes have been driven in a Volkswagen Golf with GPS tracking and logging of vehicle engine management system outputs.
I have downloaded 17580412-MM-itn.gml.gz from the OS website and used ArcGIS Productivity Suite v3.0 to convert the contents to a Geo-Database. Using the same software I used the Prepare ITN Data for Network Analyst tool to create a network dataset that can be used within ArcMap. I built the network using all the available turn restrictions, routing information, etc.
The problem I am encountering is as follows: -
When navigation restrictions are enabled, the Network Analyst cannot find a route between two points that are relatively close together. This seems to be occurring at (seemingly) random roadlink connections throughout the entire dataset be it junctions or sections of motorway. Without navigation restrictions enabled, the network analyst can find a route but only by going back on itself. I have linked two screenshots of the problem below.
I have rebuilt the network several times and have repeated the productivity suite extractions but I keep encountering the same problems in the same parts of the network.
I would appreciate any assistance you can offer me in resolving the problems outlined above.
Screenshot 1: https://picasaweb.google.com/lh/photo/9n9znTpWms-B8TLmCNRsnXVvlQ0Bm6UBfNMyJbqbgQQ?feat=directlink
Screenshot 2: https://picasaweb.google.com/lh/photo/e0Fz6wZmesLZCdpGYRWDhnVvlQ0Bm6UBfNMyJbqbgQQ?feat=directlink
It has taken us some time to process and load the information you very helpfully supplied. Initial we checked the data and I can confirm that the data is correct.
The problems you have encountered appear to be due to the way your software has processed the data, as it has not recognised that the roads in question are actually on different gradients, so it thinks there is nowhere else to go. We are not sure how to resolve this, but we have passed this information on to the account manager for the software supplier in question as feedback.
So in this instance we would recommend that you contact your software supplier for further assistance as they may be familiar with the issue and able to offer advice on how to overcome it.
I hope that this information helps to explain why we believe you have encountered the problem and reassures you that of the data integrity.
If a solution presents itself or there is any news from the account manager at a later stage we will be happy to pass on any hints and tips.