"David ``Smith''" <vidthe...@gmail.com> writes: > On Fri, Nov 27, 2009 at 2:18 AM, Dale Puch <dale.p...@gmail.com> wrote: >> It sounds like t...@home needs to trim data at the tile border, and then >> close open ways along the border of the tile... >> Just my uneducated opinion. > > Let's say you have a tile with two ways crossing it, and they don't > intersect in the tile. Both of these ways are "outer" members of the > same multipolygon relation, and they don't share any nodes. There's > no way to determine whether to color in the space between the two > ways, versus the rest of the tile except for that space, unless the > renderer knows whether the ways wrap around the polygon clockwise or > counterclockwise. One might think that it's safe to assume (as with > coastlines) the answer is clockwise, but when multipolygons are used > to map adjacent features with shared ways, that condition cannot be > true for both/all multipolygon relations; so that assumption must be > thrown out. In order to paint the polygon correctly, the entire > polygon must be known, which means loading the entire multipolygon > relation*.
Well, it would be fairly easy if the ways in a multipolygon were required to be ordered. Then, when there is a gap a renderer could just connect the ways. At least this would work in most cases. It doesn't work when the area is being inverted or becomes self-intersecting when you do that. Matthias _______________________________________________ Talk-us mailing list Talk-us@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-us