On Sun, Oct 4, 2009 at 4:55 PM, Richard Weait <[email protected]> wrote:
> If someone had mapped that intersection as a simple divided-undivided > it would be correct. Adding the four flares would also be correct. > We're building an abstraction of the real world, not a 1:1 exact > replica; where would we put it? And different mappers will disagree > on exactly where my abstract model is too much or yours is not enough. If you are creating a visual model, such as a map that would be printed out on paper, you can get away with simplification of roadways and intersections. If however the model you are creating could be used by computers to create routes, then the model needs to be specific enough to not allow the routing engine to try and send the user down the wrong roads, or ask them to perform illegal turns or such. > In either case using turn restrictions makes the abstract junction > more accurate to routing programs. You appear to be using > way-placement to imply turn restrictions. I have done that before, > but only where physical barriers exist Which is the case here. There are concrete barriers in place that would make it very difficult to travel straight through the intersection. There is a small island forcing traffic to the left, and in the middle of the intersection, another small barrier that would make it difficult to get out of the left hand turn, and continue straight. The Yahoo imagery is not of high enough detail to be able to make out the barriers, but you can see the rubber left on the road surface where the traffic is forced to travel. > I'm not saying that you are wrong, just that my choice of abstraction > allows me to be lazier for the Cragavon intersection. ;-) I'm not wrong yet... the map is an import from the GeoBase data. It has errors in it as far as I am concerned for this intersection, but I have not yet figured out how to go about making it better. > And that I should use turn restrictions for interesting junctions. ;-) > http://wiki.openstreetmap.org/wiki/Relation:restriction I would consider using these turn restrictions for intersections where the restrictions are simply legal restrictions imposed by signage/bylaws. With physical barriers in place, it makes me want to show a physical representation. A turn restriction on a simple roadway intersection node would probably work well for the routing engines, but leave some ambiguity for a printed version of the map. While everyone has different interpretations of how to depict the same physical entity, the OSM project would really benefit from having some type of uniformity. If the map is to be used by someone who is not intimately familiar with OSM mapping, they have to try and figure out how to interpret what they see on the map, and convert that to what they will find on the ground. When the same type of intersection is depicted 20 different ways in the OSM map, it makes if impossible for the user to figure out what they will be coming upon next. We should as a whole endeavor to try and come up with a fairly uniform method of depicting ways found on the ground in the OSM database. I spend a lot of time digging though the Wiki trying to make sure that the tags I am using match up with that which I am trying to map. I also rely on the collective knowledge of the users out there to help me make the right choices. I await your response now that I have clarified that this intersection does indeed have physical barriers in place restricting traffic flow. James VE6SRV _______________________________________________ newbies mailing list [email protected] http://lists.openstreetmap.org/listinfo/newbies
