[mapserver-users] Raster data performance

[Alexandre Dube]

Hi Tobi,

   The following documentation topics about raster might help :

http://mapserver.org/input/raster.html#rasters-and-tile-indexing
http://mapserver.org/input/raster.html#raster-display-performance-tips

   and about expressions :

http://mapserver.org/mapfile/expressions.html

   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.

Kind regards,

Alexandre


On 10-07-28 04:54 AM, Tobias Weiß wrote:
> Hello list,
>
> 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 ;-)
>
> 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). I use 
> TileCache to prerender maptiles for different zoom levels that are 
> later displayed in a web application using OpenLayers.
>
> 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.
>
> CLASS
>    EXPRESSION ([pixel]>= -4 AND [pixel]<  -3)
>      STYLE
> 	COLOR 69 117 180
>     END
> END
>    
>
> 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.
>
> Can anybody give me a hint how I could improve this?
>
> Best, Tobi
>
>
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> mapserver-users at lists.osgeo.org
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>    


-- 
Alexandre Dubé
Mapgears
www.mapgears.com

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