Hi, John Smith wrote: > You are confusing things,
[...] > So a straight line in the database as on the planet will still be a > straight line, We were discussing what exactly a straight line was. There is no such thing as a "straight line in the database", because, as you correctly state, the database only stores the end points of a line. If you draw a line from point lat=10;lon=10 to lat=30;lon=30, then it is unclear whether that line visits point lat=20;lon=20. Some might think yes, some might think no. * If you have drawn this line in an editor from a satellite imagery background and your editor displayed things in Mercator, then the line that you saw on the screen when you entered the two end points will *not* go through that point. * If your editor was using EPSG:4326 then the line you saw on the screen *will* go through that point. That is the problem we are talking about, not... > if the rendering software needs more points it needs to > deal with it. ... simple two-dimensional line drawing algorithms. Unless you add extra tags to the way which tell the renderer how to interpolate between the two points, there is not enough information to know. Now either we provide that information, by making a rule and hoping everyone understands and adheres to it (unlikely), or else we just try and keep our nodes close enough to each other because that will then reduce the error introduced by the ambiguity discussed above, to something that we do not have to care about. Also, just in case that has not become clear enough already, our "map" API call does not catch lines that intersect the bounding box without nodes in between, so any editor/renderer relying on this API call will not even get a chance to "deal with it" because the software won't even know that there is a line to be drawn. This is another reason why keeping your node distances in the < 5km range makes a lot of sense. I hope this has made things clearer for you. Bye Frederik _______________________________________________ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
