[mapserver-users] Display performance

[thomas bonfort]

On Fri, Sep 3, 2010 at 11:12, Chris Jackson <webturtles at gmail.com> wrote:
> Hi Jukka
>
> Thanks for the response and the great investigative work!
> My log entry for drawing the layer is - [Fri Sep 03 10:01:25 2010].658000
> msDrawMap(): Layer 1 (meanspringpeakflow), 24.500s. :o(
>
> I do wonder if my Mapfile layer definition is just v.poor (admittedly no
> expert!) so have taken an excerpt of the layer defintion (there are about 15
> classes in all) - views anyone, should I be loading it a different way?
>
> Also Jukka, could I get a sample of your scale dependent WMS GROUP layer map
> code - as it sounds like a great idea maybe for this but also some v.hi-res
> model grids I am thinking about.
>
> Thanks again, much appreciated!
> Chris
>
> LAYER
>   NAME "meanspringpeakflow"
>   TYPE polygon
>   DEBUG 5
>   DATA "Tide"
>   TEMPLATE void
>   PROJECTION
>    "+proj=utm +zone=31 +ellps=GRS80 +units=m +no_defs"
>   END
>   METADATA
>     "DESCRIPTION" "Mean Spring Peak Flow"
>     "RESULT_FIELDS" "ID,DISTANCE,DEPTH,MEAN_SP_PC"
>     "RESULT_HEADERS" "ID,Minimum Distance (m),Average Depth (m),Mean Spring
> Peak Flow (m/s)"
>     "ows_title"      "meanspringpeakflow"
>     "RESULT_HYPERLINK" "ID|| Load graphing tool"
>   END  # Metadata
>         CLASS
>             NAME '> 4.00 (m/s) '
>             EXPRESSION ([MEAN_SP_PC] >= 4 AND [MEAN_SP_PC] < 4.5)
>             STYLE
>                 COLOR 135 99 64
>             END #end style
>         END # end class
>         CLASS
>             NAME '3.51 - 4.00'
>             EXPRESSION ([MEAN_SP_PC] >= 3.5 AND [MEAN_SP_PC] < 4)
>             STYLE
>
>                 COLOR 158 126 63
>             END #end style
>         END # end class
> etc etc
>

you can speed things up a little by simplifying your expressions in
case mean_sp_pc is a continous value:

class
  expression ([item]>=4)
  ...
end
class
  expression ([item]>=3.5)  #this suffices and implies [item] <4 as
all entries with [item]>=4 wil have been treated by the first class
  ...
end
class
   ...etc...
end


regards,
thomas


>
> On 3 September 2010 09:04, Rahkonen Jukka <Jukka.Rahkonen at mmmtike.fi> wrote:
>>
>> Hi,
>>
>> I took some numbers to compare with.
>>
>> Material and methods
>>
>> Polygon layer, rather simple polygons with few vertises, Feature Count:
>> 117383
>> DEBUG 5 in mapfile
>> WMS client asks for the whole layer
>> Mapserver 5.2.1 (CGI) on not so fast Windows computer
>> Results
>> First request: rendering time taken from the log file are between 3.5 and
>> 4.5 seconds
>> Following request, BBOX is changing but all the polygons are drawn
>> though:  rendering times 1.5 - 2.5 seconds
>>
>> Conclusions and discussion
>> At first one might think that my server is faster.  But this test is not
>> controlled at all because we are not using the same shapefiles and we can't
>> say so. What we can say that a couple of hundred of thousand polygons can be
>> drawn faster.
>>
>> However, it does not really make sense to render an image this way if it
>> should be fast.  If the screen has 1000 by 1000 pixels it makes a million
>> pixels together.  For 200000 polygons it makes 5 pixels per polygon.  You
>> can simplify your polygon geometries pretty much before anybody can see the
>> differense.  If the polygons are spread evenly nobody can even see the
>> difference if there are 20000 or 200000 polygons on the screen.
>>
>> We have one polygon layer with about million polygons and for that I made
>> two simplified layers which contain only 1 percent and 10 percent of all the
>> polygons.  Those and the original shapefile are put into the same scale
>> dependent WMS GROUP layer. This group is pretty fast at any scale.  The 1
>> percent layer is perhaps a bit too sparse but I have been too lazy to have a
>> try with 2 or 5 percent samples.
>>
>> -Jukka Rahkonen-
>
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