2010/1/9 Frederik Ramm <[email protected]>: > * If your editor was using EPSG:4326 then the line you saw on the screen > *will* go through that point.
Most imagery, if not all, used for this purpose will be EPSG:4326, ie lat/lon, and the co-ords uploaded to OSM is lat/lon, and ways are a collection of points, they don't have their own co-ords... > ... 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. Why isn't there? mapnik etc convert from lat/lon to x/y before drawing, so they could easily add extra x/y points when the conversion process happens. > 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. Except for the fact that OSM only accepts lat/lon, the x/y happens during preprocessing before mapnik gets it, if extra points are needed the preprocessor can generate them. > 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. No it isn't, the preprocessing software could do that if it needs it, this isn't a reason to add extra nodes to the database. _______________________________________________ talk mailing list [email protected] http://lists.openstreetmap.org/listinfo/talk
