[mapserver-users] Raster data performance

[Tobias Weiß]

Thanks, David. I will try if this will bring some significant
performance boost ...
Tobi

===
Am 28.07.10 16:09, schrieb Fawcett, David (MPCA):
>
> I don't know anything about your work flow, but if possible, you could
> add a pre-processing step where you use a script to read your text
> file and pre-classify the data.  You would end up with integers
> representing each class as 'cell' values. 
>
>  
>
> Instead of :
>
> EXPRESSION([pixel] >= -4 AND [pixel] < -3)
>
>  
>
> You could have: EXPRESSION "2"
>
> Or
>
> EXPRESSION /2/
>
>  
>
> Matching a single string should be the fastest expression to evaluate.
>
>  
>
> David.
>
>  
>
> *From:* mapserver-users-bounces at lists.osgeo.org
> [mailto:mapserver-users-bounces at lists.osgeo.org] *On Behalf Of *Tobias
> Weiß
> *Sent:* Wednesday, July 28, 2010 8:25 AM
> *To:* mapserver-users at lists.osgeo.org
> *Subject:* Re: [mapserver-users] Raster data performance
>
>  
>
> 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
>
>  
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>   
>
>
>
>
> -- 
> Alexandre Dubé
> Mapgears
> www.mapgears.com <http://www.mapgears.com>
>   
>  
>  
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>   


-- 
Dipl.-Ing. Tobias Weiß
Potsdam Institute for Climate Impact Research
Pappelallee 20, Room 316
14469 Potsdam
Germany

Phone: +49 / (0)331 / 288-2490
Location: http://bit.ly/1gOr64

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