<div>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.
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<div>Linda<br><br></div>
<div class="gmail_quote">On Dec 28, 2007 7:33 AM, cmose <<a href="mailto:cjmose@gmail.com">cjmose@gmail.com</a>> wrote:<br>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid"><br>I just wanted to see if anyone had come across any more causes of the Random<br>Tile issue. I'm encountering that quite often using OL
2.6 and TileCache<br>1.9. Numerous tiles load out of sequence - typically they are copies of<br>tiles already loaded into the map (e.g., a big land mass tile showing up in<br>the middle of the atlantic, one country's capital ending up in another
<br>country due to bad tile, etc.,). I am seeing this quite frequently -<br>unfortunately I can't pop up an example site as this is an internal app.<br><br>(I'm also not seeing any spiral loading - quite typically the tiles in the
<br>middle of the screen are the last to load).<br><br>Thanks much<br><br><br><br>Christopher Schmidt wrote:<br>><br>> On Thu, Oct 05, 2006 at 09:52:49AM +0100, David Herbert wrote:<br>>> I don't see this at all. What I get is a rather random loading, and
<br>>> often a critical inside tile is last to load. And sometimes as I said<br>>> above, that tile doesn't load at all, though the WMS has served it.<br>>> Presumably the requests for tiles are fired off in separate threads
<br>>> rather than synchronously? So differences in WMS loading and response<br>>> times could theoretically mess up spiral gridding? Doesn't explain the<br>>> blank tiles though.<br>><br>> Although the problem is apparently intermittent and hard to reproduce
<br>> (neither myself, Erik, or Schuyler have ever seen it), I do want to<br>> address the issue of how the tiles are loaded.<br>><br>> Loading the actual images is not performed by OpenLayers. The mechanism<br>
> in which tiles are loaded is:<br>><br>> * Create a set of 'img' elements in a grid, and set their<br>> style.display to 'none'. An 'onload' event is attached to the image,<br>> which will unset its display style, and an onerror event is attached
<br>> which unsets its display style and changes the background color.<br>> * Start at the center of the grid and 'spiral' outward through the<br>> grid: set the img src on each image.<br>><br>
> When panning:<br>> * A column is taken from the non-visible edge of the grid, and added<br>> onto the newly panned part of the grid. The style on these tiles is<br>> set to display:none, and the tiles then have their
img.src<br>> modified.<br>><br>> The second step is probably done more quickly than any of the tiles<br>> load, and the loading of the tiles is then handled entirely by the<br>> browser.<br>><br>> So, the step to start looking is probably to add some logging in the
<br>> Tile.Image class, possibly in the 'draw' function.<br>><br>> Beyond that, I've not yet been able to reproduce this, so tracking the<br>> bug down is very hard: Is it possible that your internet connection is
<br>> relatively slow, and so the tile onload events get confused?<br>><br>> I would expect that you would *not* have gotten this behavior under 1.0<br>> or most of the pre 2.0 svn: Not until we implemented img/tile reuse.
<br>> Unfortunately, this can't just be removed -- the memory ramifications<br>> for not reusing the image elements are just too high.<br>><br>> Hopefully, this will help you begin to investigate the problem.
<br>> Unfortuantely, until I can reproduce it, I can't figure out how to help<br>> debug it.<br>><br>> Good luck, and please report back if you do find anything.<br>><br>> Regards,<br>> --<br>> Christopher Schmidt
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http://openlayers.org/mailman/listinfo/users</a><br></font></blockquote></div><br><br clear="all"><br>-- <br>Linda Rawson