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Hi Tobi,<br>
<br>
The following documentation topics about raster might help :<br>
<br>
<a class="moz-txt-link-freetext" href="http://mapserver.org/input/raster.html#rasters-and-tile-indexing">http://mapserver.org/input/raster.html#rasters-and-tile-indexing</a><br>
<a class="moz-txt-link-freetext" href="http://mapserver.org/input/raster.html#raster-display-performance-tips">http://mapserver.org/input/raster.html#raster-display-performance-tips</a><br>
<br>
and about expressions :<br>
<br>
<a class="moz-txt-link-freetext" href="http://mapserver.org/mapfile/expressions.html">http://mapserver.org/mapfile/expressions.html</a><br>
<br>
The string comparison type is the fastest, so you could try define
more classes but using string comparison to see if it gets faster.
Also, a good performance tip is to put your most frequent classes types
on top first. For example, if 80% of your data has "pixel = -3" then
put it on top.<br>
<br>
Kind regards,<br>
<br>
Alexandre<br>
<br>
<br>
On 10-07-28 04:54 AM, Tobias Weiß wrote:
<blockquote cite="mid:4C4FF051.3060309@pik-potsdam.de" type="cite">
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content="text/html; charset=ISO-8859-1">
<font face="Tahoma">Hello list,<br>
<br>
this is my first email to this list. I am working with MapServer,
OpenLayers & TileCache for almost 1 year now and the tools are
really working great together, when everything is configured correctly
;-)<br>
<br>
At the moment I´m facing a performance problem with raster data that
serves as input data to render my map tiles. The spatial resolution of
this raster data is 720 (rows) x 360 (cols) and it is stored in a
simple .txt file (The size of the file is around 2 MB). </font><font
face="Tahoma">I use TileCache to prerender maptiles for different zoom
levels that are later displayed in a web application using OpenLayers.<br>
<br>
</font><font face="Tahoma">I discovered, that the rendering speed of
MapServer seems to mainly depend on how many different classes I define
within my mapfile, meaning how many expressions MapServer has to
evaluate during the rendering process. Without any classes MapServer
the rendering speed is really fast, the more classes I use the slower
it gets. With e.g. 10 different classes defining 10 different styles /
pixel colors the rendering time for one tile can increase up to 60 sec.<br>
<br>
</font>
<pre wrap="">CLASS<span class="moz-txt-citetags">
</span>EXPRESSION ([pixel] >= -4 AND [pixel] < -3)<span
class="moz-txt-citetags">
</span>STYLE
<span class="moz-txt-citetags"></span> COLOR 69 117 180
<span class="moz-txt-citetags"></span> END
<span class="moz-txt-citetags"></span>END
</pre>
<br>
<font face="Tahoma">While working with shape files I haven´t had this
problems and prerendering map tiles was really fast. With raster data
the rendering time for one map and 5 different zoom levels can take up
to several hours and almost overburdens my CPU.<br>
<br>
Can anybody give me a hint how I could improve this?<br>
<br>
Best, Tobi<br>
</font>
<pre wrap="">
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</pre>
</blockquote>
<br>
<br>
<pre class="moz-signature" cols="72">--
Alexandre Dubé
Mapgears
<a class="moz-txt-link-abbreviated" href="http://www.mapgears.com">www.mapgears.com</a>
</pre>
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