[mapserver-users] Raster data performance

[Tobias Weiß]

Hi Alex,

I tried some of the performance tips you mentioned, e.g. converted the
.txt to a tiled TIFF to optimize performance.  I can not see significant
changes in rendering speed.

gdal_translate -co TILED=YES input.txt output.tif

The major brake still is the expression stuff. I really wonder what
makes this task so time-consuming, it should not be more than a simple
comparison.

Do you have experiences with this issue? Or do I have to live with this
constraint?

Best, Tobi

===
Am 28.07.10 14:27, schrieb 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
>>
>>
>> _______________________________________________
>> mapserver-users mailing list
>> mapserver-users at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/mapserver-users
>>   
>
>
> -- 
> Alexandre Dubé
> Mapgears
> www.mapgears.com
>   
>
>
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