[mapserver-users] WMS Client changes slightly BBOX

[Peter Hopfgartner]

Hi Worth,

thanks for your quick reply. Anyway, the ratio of the extent and of the 
image seem to match al least up to 10 digits. Playing with the numbers, 
the error is in the same order of magnitude as if I change image size by 
one pixel. I would guess, that there is a "off by 1" error somewhere in 
the MapServer code.

Regards,

Peter

On 07/24/2014 01:30 PM, Worth Lutz wrote:
> Peter,
>
> I have found that if the map size (width and height in pixels) aspect 
> ratio does not exactly match the map extents (map units) aspect ratio 
> the map extents are adjusted.
>
> I'm working with MapScript and to get exact scale pdf map I have to 
> set map size first and then extent and then scale to get good results.
>
> I hope this helps.
>
>
> *Worth Lutz*
> ------------------
>
> On 07/24/2014 06:49 AM, Peter Hopfgartner wrote:
>> I'm generating dynamically Map Object, with with a certain extent, in 
>> the concrete example
>> 629396.05065523,4984079.9894638,655192.92565523,5019084.3644638
>>
>> In generated Map object uses the WMS client functionality to call WMS 
>> services. Anyway, the BBOX get's slightly changed, so that the 
>> original scale of 1:100000 gets changed to approx 1:100103, since it 
>> calls the WMS services with
>> 629382.807906257,4984062.02007212,655206.168404203,5019102.33385548
>> as can be taken from the web server log files:
>>
>> mmm.mmm.mmm.mmm - - [24/Jul/2014:12:25:58 +0200] "GET 
>> /author/services/ows.php?PROJECT=ancitel&MAP=catasto_reti&LANG=xw&OGSTAT=ot3cp0i7qmph4guuof75702m70&RESOLUTION=96&LAYERS=dtm,uso_lombardia,strade_lombardia,g_limiti_amministrativi,g_label,g_0707,g_0704&REQUEST=GetMap&SERVICE=WMS&FORMAT=image/png%3B+mode%3D8bit&STYLES=,,,,,,&HEIGHT=1323&VERSION=1.1.1&SRS=EPSG:32632&WIDTH=975&BBOX=629382.807906257,4984062.02007212,655206.168404203,5019102.33385548&TRANSPARENT=TRUE&EXCEPTIONS=application/vnd.ogc.se_inimage 
>> HTTP/1.1" 200 678803 "-" "MapServer/6.4.1 libcurl/7.19.7"
>>
>> This change in scale is beyound te axpected tolerance in this 
>> particular use case, where technical data must be plotted in a PDF file.
>>
>> Any help is appreciated. Obvioulsly, I can fetch the WMS services in 
>> my code and overlay them "by hand". Anyway, for a couple of reasons 
>> this was the preferred approach.
>>
>> Regards,
>>
>> Peter
>>
>>
>>
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>
>
>
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-- 
Peter Hopfgartner
R3 GIS Srl - GmbH
Via Johann Kravogl-Str. 2
I-39012 Meran/Merano (BZ)
web  : www.r3-gis.com
mail : peter.hopfgartner at r3-gis.com
phone: +39 0473 494949
fax  : +39 0473 069902

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