[mapserver-users] WMS Client changes slightly BBOX

[Peter Hopfgartner]

This would be perfectly compatible with the difference on 1 pixel.

Thanks,

Peter

On 07/25/2014 12:32 AM, Lime, Steve D (MNIT) wrote:
>
> There’s a difference between the extent models used by MapServer and 
> OGC. The WMS code adjusts for that difference so the input extent will 
> definitely see adjustment to account for that. OGC uses the UL corner 
> of the UL pixel and the LR corner of the LR pixel. MapServer uses 
> pixel centers consistently. Do your scale computations account for 
> this difference?
>
> Steve
>
> *From:*mapserver-users-bounces at lists.osgeo.org 
> [mailto:mapserver-users-bounces at lists.osgeo.org] *On Behalf Of *Peter 
> Hopfgartner
> *Sent:* Thursday, July 24, 2014 7:20 AM
> *To:* mapserver-users at lists.osgeo.org
> *Subject:* Re: [mapserver-users] WMS Client changes slightly BBOX
>
> 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
web  : http://www.r3-gis.com

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