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
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