Detail displey when zoom in

[Fawcett, David]

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.  
 
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.  
 
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.  
 
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.  
 
David.

	-----Original Message-----
	From: UMN MapServer Users List
[mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On Behalf Of Bruno Patini Furtado
	Sent: Monday, August 14, 2006 7:50 AM
	To: MAPSERVER-USERS at LISTS.UMN.EDU
	Subject: Re: [UMN_MAPSERVER-USERS] Detail displey when zoom in
	
	
	One thing that might help is knowing that the MapServer
terminology for zoom is Overviews as can be seen in
http://mapserver.gis.umn.edu/docs/howto/raster_data/#building-internal-o
verviews .
	
	Also, the GDAL uses the same term in
http://www.gdal.org/gdaladdo.html where:
	
	The gdaladdo utility can be used to build or rebuild overview
images for most supported file formats with one over several
downsampling algorithms.
	

	On 8/13/06, Hooi <wchoonhooi at gmail.com> wrote: 

		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?
		




	-- 
	"Minds are like parachutes, they work best when open."
	
	Bruno Patini Furtado
	Software Developer
	webpage: http://bpfurtado.net 
	software development blog: http://bpfurtado.livejournal.com 

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