Re: [UMN_MAPSERVER-USERS] Detail displey when zoom in

Mon, 14 Aug 2006 07:11:53 -0700

Thanks for the clarification :)

On 8/14/06, Fawcett, David <[EMAIL PROTECTED]> wrote:
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:[email protected]] On Behalf Of Bruno Patini Furtado
Sent: Monday, August 14, 2006 7:50 AM
To: [email protected]
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-overviews .

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 <[EMAIL PROTECTED]> 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



--
"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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