On Fri, Sep 14, 2007 at 11:40:25AM -0700, Chris Hodgson wrote: > I see that someone else has already documented something closely related > to this issue: > > http://crschmidt.net/blog/archives/154/mapserver-rendering-bug/ > > And that it has already been solved in tilecache by adding a buffer > around the meta-tiles during rendering - but I don't think that solution > will help with the single-pixel-wide line. Meta-tiling and/or increasing > the size of the tiles would reduce the likelihood of this happening, but > I don't think they could prevent it.
It would prevent it, because the problem only presents itself at tile edges -- and the data from MapServer no longer *has* any visible tile edges in a meta-tiled TileCache instance. To see similar behavior to TileCache metatiling, set the 'gutter' option on your WMS layer to '15' or something similar (see http://openlayers.org/dev/examples/gutter.html) and I bet you'd see the problem disappear. > Rendering oversize tiles/meta-tiles > and cropping them wouldn't have any effect, unless you were using > anti-aliasing, in which case the problem might be reduced to the line > getting more faint as it crossed the edge, but still I don't think that > the line would be properly rendered. If you're not convinced, try the gutter option. If that doesn't fix it, you'd be right -- but I bet it will. > I suppose this might be considered a minor issue because of how rarely > one would expect to have their lines be nearly parallel to and cross the > tile boundaries, but I've actually seen that it can happen on just about > any line that crosses a tile boundary at an acute angle. I certainly don't consider this bug to be minor issue, but I wrote code to fix the problem, so I would assume that's obvious ;) Regards, -- Christopher Schmidt MetaCarta
