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<DIV><SPAN class=427171413-14082006><FONT face=Arial color=#0000ff size=2>I
would say that zoom is still meaningful in describing MapServer. When you
'zoom', you either request a layer that shows more (or less) earth area in your
fixed-size map window. </FONT></SPAN></DIV>
<DIV><SPAN class=427171413-14082006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=427171413-14082006><FONT face=Arial color=#0000ff
size=2>Overviews do not relate directly to the map image being returned by
MapServer. They are used as part of a raster data source to help make your
application more efficient. An overview is useful when you have images
that have a high resolution and you want to use as a data layer on a relatively
low resolution map. </FONT></SPAN></DIV>
<DIV><SPAN class=427171413-14082006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=427171413-14082006><FONT face=Arial color=#0000ff size=2>For
example, if you have an air photo that is 1,000,000 x 1,000,000 pixels and you
want to use it at full extent in your map image that is 100 x 100 pixels.
Every time that you request a map image, MapServer or one of it's components has
to look at the big image and figure out what color to make each of the pixels in
the 100 x 100 pixel layer. That takes a lot of processing.
</FONT></SPAN></DIV>
<DIV><SPAN class=427171413-14082006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=427171413-14082006><FONT face=Arial color=#0000ff
size=2>Instead, you can pre-build overviews, either inside or outside of the
image file for your data layer. That way, when you request a map image
like above, MapServer (or OGR) can decide to just use the pre-built
overview. </FONT></SPAN></DIV>
<DIV><SPAN class=427171413-14082006><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=427171413-14082006><FONT face=Arial color=#0000ff
size=2>David.</FONT></SPAN></DIV>
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<DIV></DIV>
<DIV class=OutlookMessageHeader lang=en-us dir=ltr align=left><FONT
face=Tahoma size=2>-----Original Message-----<BR><B>From:</B> UMN MapServer
Users List [mailto:MAPSERVER-USERS@LISTS.UMN.EDU] <B>On Behalf Of </B>Bruno
Patini Furtado<BR><B>Sent:</B> Monday, August 14, 2006 7:50 AM<BR><B>To:</B>
MAPSERVER-USERS@LISTS.UMN.EDU<BR><B>Subject:</B> Re: [UMN_MAPSERVER-USERS]
Detail displey when zoom in<BR><BR></FONT></DIV>One thing that might help is
knowing that the MapServer terminology for zoom is Overviews as can be seen in
<A
href="http://mapserver.gis.umn.edu/docs/howto/raster_data/#building-internal-overviews">http://mapserver.gis.umn.edu/docs/howto/raster_data/#building-internal-overviews
</A>.<BR><BR>Also, the GDAL uses the same term in <A
href="http://www.gdal.org/gdaladdo.html">http://www.gdal.org/gdaladdo.html</A>
where:<BR>
<DIV style="MARGIN-LEFT: 40px"><SPAN style="FONT-STYLE: italic">The gdaladdo
utility can be used to build or rebuild overview images for most supported
file formats with one over several downsampling
algorithms.</SPAN><BR></DIV><BR>
<DIV><SPAN class=gmail_quote>On 8/13/06, <B class=gmail_sendername>Hooi</B>
<<A href="mailto:wchoonhooi@gmail.com">wchoonhooi@gmail.com</A>>
wrote:</SPAN>
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style="PADDING-LEFT: 1ex; MARGIN: 0pt 0pt 0pt 0.8ex; BORDER-LEFT: rgb(204,204,204) 1px solid">
<DIV>I intend to do something like Google Local where when user zoom in, he
can see same area but more details. How can I achieve this in
Mapserver?<BR></DIV></BLOCKQUOTE></DIV><BR><BR clear=all><BR>-- <BR>"Minds are
like parachutes, they work best when open."<BR><BR>Bruno Patini
Furtado<BR>Software Developer<BR>webpage: <A
href="http://bpfurtado.net">http://bpfurtado.net </A><BR>software development
blog: <A
href="http://bpfurtado.livejournal.com">http://bpfurtado.livejournal.com</A>
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