Just to add some more info to this topic. I had very strange behavior when I switched the tilecaching to a linux box running with mod_python. I never saw the problem using CGI. That could have been a speed problem or something else. In addition I also found a slight problem when openlayers sends the url encoded string to the WMS service. Some handle them and some do not.
Linda On Dec 28, 2007 7:33 AM, cmose <[EMAIL PROTECTED]> wrote: > > I just wanted to see if anyone had come across any more causes of the > Random > Tile issue. I'm encountering that quite often using OL 2.6 and TileCache > 1.9. Numerous tiles load out of sequence - typically they are copies of > tiles already loaded into the map (e.g., a big land mass tile showing up > in > the middle of the atlantic, one country's capital ending up in another > country due to bad tile, etc.,). I am seeing this quite frequently - > unfortunately I can't pop up an example site as this is an internal app. > > (I'm also not seeing any spiral loading - quite typically the tiles in the > middle of the screen are the last to load). > > Thanks much > > > > Christopher Schmidt wrote: > > > > On Thu, Oct 05, 2006 at 09:52:49AM +0100, David Herbert wrote: > >> I don't see this at all. What I get is a rather random loading, and > >> often a critical inside tile is last to load. And sometimes as I said > >> above, that tile doesn't load at all, though the WMS has served it. > >> Presumably the requests for tiles are fired off in separate threads > >> rather than synchronously? So differences in WMS loading and response > >> times could theoretically mess up spiral gridding? Doesn't explain the > >> blank tiles though. > > > > Although the problem is apparently intermittent and hard to reproduce > > (neither myself, Erik, or Schuyler have ever seen it), I do want to > > address the issue of how the tiles are loaded. > > > > Loading the actual images is not performed by OpenLayers. The mechanism > > in which tiles are loaded is: > > > > * Create a set of 'img' elements in a grid, and set their > > style.display to 'none'. An 'onload' event is attached to the image, > > which will unset its display style, and an onerror event is attached > > which unsets its display style and changes the background color. > > * Start at the center of the grid and 'spiral' outward through the > > grid: set the img src on each image. > > > > When panning: > > * A column is taken from the non-visible edge of the grid, and added > > onto the newly panned part of the grid. The style on these tiles is > > set to display:none, and the tiles then have their img.src > > modified. > > > > The second step is probably done more quickly than any of the tiles > > load, and the loading of the tiles is then handled entirely by the > > browser. > > > > So, the step to start looking is probably to add some logging in the > > Tile.Image class, possibly in the 'draw' function. > > > > Beyond that, I've not yet been able to reproduce this, so tracking the > > bug down is very hard: Is it possible that your internet connection is > > relatively slow, and so the tile onload events get confused? > > > > I would expect that you would *not* have gotten this behavior under 1.0 > > or most of the pre 2.0 svn: Not until we implemented img/tile reuse. > > Unfortunately, this can't just be removed -- the memory ramifications > > for not reusing the image elements are just too high. > > > > Hopefully, this will help you begin to investigate the problem. > > Unfortuantely, until I can reproduce it, I can't figure out how to help > > debug it. > > > > Good luck, and please report back if you do find anything. > > > > Regards, > > -- > > Christopher Schmidt > > Web Developer > > _______________________________________________ > > Users mailing list > > [email protected] > > http://openlayers.org/mailman/listinfo/users > > > > > > -- > View this message in context: > http://www.nabble.com/strange-problems-with-out-of-sequence-out-of-range-map-tiles-tp6603260p14526518.html > Sent from the OpenLayers Users mailing list archive at > Nabble.com<http://nabble.com/> > . > > _______________________________________________ > Users mailing list > [email protected] > http://openlayers.org/mailman/listinfo/users > -- Linda Rawson
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