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<font face="Times New Roman">Interesting. Could this be added to the
documentation? It's important when you are scaling at pixel level.
Would it make sense to add an option for MapServer to treat
extents the same way as GDAL?<br>
<br>
Jan<br>
</font><br>
On 2011-02-17 16:07, Lime, Steve D (DNR) wrote:
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<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">It’s due to how MapServer interprets extents. It
uses a pixel-center model so you end up using width or
height minus one in computations because<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">an extent is from the center of the UL pixel to
the center of LR pixel (you lose the “one” from the outside)
. I’ve attached a graphic I created some time<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">ago that illustrates the difference between a
MapServer extent and the model GDAL and WMS use.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">Steve<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size: 10pt;
font-family: "Tahoma","sans-serif";">From:</span></b><span
style="font-size: 10pt; font-family:
"Tahoma","sans-serif";">
<a class="moz-txt-link-abbreviated" href="mailto:mapserver-dev-bounces@lists.osgeo.org">mapserver-dev-bounces@lists.osgeo.org</a>
[<a class="moz-txt-link-freetext" href="mailto:mapserver-dev-bounces@lists.osgeo.org">mailto:mapserver-dev-bounces@lists.osgeo.org</a>] <b>On
Behalf Of </b>Mohamed Saâd HESSANE<br>
<b>Sent:</b> Thursday, February 17, 2011 4:41 AM<br>
<b>To:</b> <a class="moz-txt-link-abbreviated" href="mailto:mapserver-dev@lists.osgeo.org">mapserver-dev@lists.osgeo.org</a><br>
<b>Subject:</b> [mapserver-dev] Implementation of the
msCalculateScale<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Good morning everybody.<br>
I don't understand how the msCalculateScale function in
mapscale.c is implemented.<br>
As far as I know, the scale is calculated from the relation :
inches_in_screen / inches_in_reallity.<br>
inches_in_screen : depend on the DPI and the width of the map;<br>
inches_in_reality : depend on the map.extent, and the pixel
size.<br>
So why the "width-1" at the line 96? For me just "width" is
more correct. Perhaps I'm wrong.<br>
The branches 4.X have just "width" in their implementations
(line 125).<br>
So why the center pixel is removed from calculation?<o:p></o:p></p>
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