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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">MapServer compares the requested extent to the aspect ratio of requested image. The code (msAdjustExtent in maputil.c) starts by computing a cellsize in each
direction (x and y) and then uses the largest value to pad the other. You’re guaranteed to preserve the extent in one of the direction and maybe both.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Steve<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> mapserver-users-bounces@lists.osgeo.org [mailto:mapserver-users-bounces@lists.osgeo.org]
<b>On Behalf Of </b>Zach Chehayeb<br>
<b>Sent:</b> Thursday, October 01, 2015 3:22 PM<br>
<b>To:</b> Basques, Bob (CI-StPaul) <bob.basques@ci.stpaul.mn.us><br>
<b>Cc:</b> mapserver-users@lists.osgeo.org<br>
<b>Subject:</b> Re: [mapserver-users] Understanding extents and resolutions<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Bob,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">I am not sure I am understanding your response correctly. Are you suggesting that it is the coordinate window ratio that determines whether mapserver locks on
the east/west or north/south bounds? If so, this doesn’t align with my observations below as all the images where sent the exact same coordinate window but pad on a different axis.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">I plan to do the computation to match up exactly as you have suggested but I want to be sure that I correctly understand the logic that mapserver uses to decide
which axis to pad so I can apply the computations to the correct axis. I have to maintain backward compatibility in my application and need to accurately assess the actual extent drawn.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Zach Chehayeb<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Application Developer<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Email.
<a href="mailto:zach.chehayeb@airborne.aero">zach.chehayeb@airborne.aero</a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Tel No. +1 949 707 1800<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><a href="www.airborne.aero">www.airborne.aero</a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><img border="0" width="106" height="29" id="Picture_x0020_2" src="cid:image001.gif@01D0FC5E.0DDBAC10" alt="New Small2"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma",sans-serif">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma",sans-serif"> Basques, Bob (CI-StPaul) [<a href="mailto:bob.basques@ci.stpaul.mn.us">mailto:bob.basques@ci.stpaul.mn.us</a>]
<br>
<b>Sent:</b> Thursday, October 01, 2015 12:29 PM<br>
<b>To:</b> Zach Chehayeb<br>
<b>Cc:</b> <a href="mailto:mapserver-users@lists.osgeo.org">mapserver-users@lists.osgeo.org</a><br>
<b>Subject:</b> Re: [mapserver-users] Understanding extents and resolutions<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Zach, <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">If I’m understanding your question correctly, MapServer will always give you your requested coordinate space inside of the requested image size, by buffering the image results along the axis that is larger than the coordinate window needs
to draw completely. In other words, MapServer automatically pads the output image to fill in those areas, East/West and North/South edges based on the coordinate space requested.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">If you need them to match up exactly, then you need to do the computations in your application to make the correct requests and make the coordinate window ratio match the pixel window (image size) ratios.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">bobb<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Oct 1, 2015, at 2:13 PM, Zach Chehayeb <<a href="mailto:zach.chehayeb@airborne.aero">zach.chehayeb@airborne.aero</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">Hello All,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">Can anyone explain or point me in the right direction on how mapserver logic works when a requested map extent cannot be produced at the requested resolution with square pixels?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">I am using mapserver in an application that requests mapserver to produce various map extents at various resolutions. The map config is set to not allow non square pixel (so
the MS_NONSQUARE setting is set to no). The application currently assumes that the extent height should always be half of the width. Of course, with MS_NONSQUARE set to no and producing resolutions where the height is not always exactly half of the width,
mapserver is unable to produce the exact extents requested. As such, mapserver compensates by extending either the north and south or east and west bounds of the map. See images in link below for a detailed illustration (the red box indicates the requested
extent). For all images below, the requested extent is x1=-58.615527, y1=50.434875, x2=-13.615527, y2=72.934875, but the actual extents differ.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From my observations, it seems that there are three cases. I have included a link below where a zip file that has examples of the cases can be downloaded.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"><a href="https://www.dropbox.com/s/dy1cgmt8lmbl3wf/Example%20Images.zip?dl=0"><span style="color:purple">https://www.dropbox.com/s/dy1cgmt8lmbl3wf/Example%20Images.zip?dl=0</span></a><o:p></o:p></span></p>
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<p class="MsoNormal" style="text-indent:-.25in"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">1.</span><span style="font-size:7.0pt"> <span class="apple-converted-space"> </span></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">The
requested resolution height is greater than half of the width (1280x720).<o:p></o:p></span></p>
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<p class="MsoNormal" style="text-indent:-.25in"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">a.</span><span style="font-size:7.0pt"> <span class="apple-converted-space"> </span></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">Result:
MapServer locks on the East and West bounds and extends the North and South bounds of the map.<o:p></o:p></span></p>
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<p class="MsoNormal" style="text-indent:-.25in"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">2.</span><span style="font-size:7.0pt"> <span class="apple-converted-space"> </span></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">The
requested resolution height is less than half of the width (960x400).<o:p></o:p></span></p>
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<p class="MsoNormal" style="text-indent:-.25in"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">a.</span><span style="font-size:7.0pt"> <span class="apple-converted-space"> </span></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">Result:
MapServer locks on the North and South bounds and extends the East and West bounds.<o:p></o:p></span></p>
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<p class="MsoNormal" style="text-indent:-.25in"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">3.</span><span style="font-size:7.0pt"> <span class="apple-converted-space"> </span></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">The
requested resolution height is half of the width (1000x500).<o:p></o:p></span></p>
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<p class="MsoNormal" style="text-indent:-.25in"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">a.</span><span style="font-size:7.0pt"> <span class="apple-converted-space"> </span></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">Result:
MapServer produces the image at the requested resolution.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">Is anyone able to confirm that these are the only three cases or correct my understanding (if there is more to it than I have described)?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">Some info about my installation:<o:p></o:p></span></p>
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<p class="MsoNormal" style="text-indent:-.25in"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">1.</span><span style="font-size:7.0pt"> <span class="apple-converted-space"> </span></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">MapServer
version 6.0.3 OUTPUT=GIF OUTPUT=PNG OUTPUT=JPEG SUPPORTS=PROJ SUPPORTS=AGG SUPPORTS=FREETYPE SUPPORTS=ICONV SUPPORTS=FRIBIDI SUPPORTS=WMS_SERVER SUPPORTS=WMS_CLIENT SUPPORTS=WFS_SERVER SUPPORTS=WFS_CLIENT SUPPORTS=FASTCGI SUPPORTS=THREADS INPUT=OGR INPUT=GDAL
INPUT=SHAPEFILE<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">Please let me know if there is any other information needed.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">Thanks in advance,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">Zach Chehayeb<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">Application Developer<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">Email.<span style="color:#1F497D"> </span><a href="mailto:zach.chehayeb@airborne.aero"><span style="color:purple">zach.chehayeb@airborne.aero</span></a><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">Tel No. +1 949 707 1800<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"><a href="x-msg://46/www.airborne.aero"><span style="color:purple">www.airborne.aero</span></a><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"> </span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><image001.jpg></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"ComicSansMS",serif">_______________________________________________<br>
mapserver-users mailing list<br>
</span><a href="mailto:mapserver-users@lists.osgeo.org"><span style="font-size:9.0pt;font-family:"ComicSansMS",serif;color:purple">mapserver-users@lists.osgeo.org</span></a><span style="font-size:9.0pt;font-family:"ComicSansMS",serif"><br>
</span><a href="http://lists.osgeo.org/mailman/listinfo/mapserver-users"><span style="font-size:9.0pt;font-family:"ComicSansMS",serif;color:purple">http://lists.osgeo.org/mailman/listinfo/mapserver-users</span></a><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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