Cygnus is the Telenav Mapping conflation tool. We use it a lot internally to compare approved external data sources with existing OSM data, but there is also a public version. We outlined how it works in an earlier blog post. In this post, I want to highlight some of the newer features in Cygnus. These new features are based on the feedback from our team of Map Analysts, who use the tool in their day to day work.
Discarding Very Short Segments
Cygnus outputs the differences in geometry between existing OSM data and the spatial data that we want to use to improve OSM. Sometimes, when the differences are very tiny, Cygnus used to export very short ways. These are not really meaningful enhancements, and clutter up the result data. Therefore, we implemented a length filter. Ways shorter than a defined length threshold will not be included in the output. Based on experience, we set the default to 5 meters. In the internal (command line) version our team uses, this can be tweaked using a parameter. In the public web version, this is not yet possible. We can consider adding it if there is sufficient demand.
When comparing road geometry, Cygnus not only compares geometry, but also road names. An annoying side effect we noticed is that road names are often not exactly the same in OSM as they are in the external data we compare with. This does not mean that the external data is necessarily better. For example, OSM could say that the name of a road is “River Road”, and the external data source could say it is “River Rd”. This is not a meaningful difference, and we would want to exclude those in most cases. So we added a string distance based threshold in Cygnus to filter out similar strings. It is set to a sensible default which, again, can be tweaked in the command line version we use internally, but not yet in the web version.
Another Cygnus improvement related to road names is to ignore name differences on certain types of ways: roundabouts and service roads. Roundabout ways in OSM do not have names by convention, unless the roundabout itself has a name, so they should generally not be added. Service roads technically can have names in OSM, but it is not common. In external data, they do sometimes have names, but if they do, it usually does not make sense to add them to OSM. Based on our experience, they often have descriptive names like ‘driveway’ or ‘access road’ in the source data.
You can use Cygnus yourself by going to http://cygnus.improve-osm.org/ and uploading your source data file. You need to do a fair amount of work to prepare the source data: translating the source attributes into valid OSM tags, and converting to OSM PBF. And always remember to consider carefully what you do with the result. Cygnus is not designed to be an automated import tool. Every suggested change should be manually reviewed.
Let us know how you have used, or would like to use Cygnus!