Frank,
We currently have the whole earth split into 4 files using 1Km resolution Blue
Marble) images.
There are overviews in the images we are currently using but these do not match
exactly the output resolution we need they will be resized so there is a hit
there. We are trying to work out how to resize the overviews so that there is
an exact match the zoom levels we are using but our attempts yesterday did not
work as I could not make sense of how gdalallo scales the overviews.
Also does anyone out there understand how the image save process works? We are
using php mapscript and the saveImage function takes longer than we would
expect compared to other image utilities/programs we are using on the same
hardware. We do not need any specific image format and do not require
compression so the image save should be very quick.
Thanks
Ian
-Original Message-
From: fwarmer...@gmail.com [mailto:fwarmer...@gmail.com] On Behalf Of Frank
Warmerdam
Sent: Friday, November 11, 2011 11:52 AM
To: Ian Walberg
Cc: mapserver-users@lists.osgeo.org
Subject: Re: [mapserver-users] Raster image performance
Ian,
I am guessing you actually have many files, not just one big one. Is that
right? As you zoom out opening many files to
accumulate the full image is expensive. Up to some scale
it is practical to merge things into one big mosaic tiff with overviews.
At some point that can be impractically large.
The usual practice to avoid opening too many files with tileindexed layers is
to have two LAYERs in your map file. One for the fuller resolution data, and
then another at greatly reduced resolution and then to generate a reduced
resolution mosaic for the reduced resolution layer. Use the MIN/MAX SCALE
control keyword in the LAYER to control which is used.
Best regards,
On Fri, Nov 11, 2011 at 11:15 AM, Ian Walberg wrote:
> Does anyone have any experience of how to get the best performance out
> of raster formats.
>
> We have an application which needs to be able to display a number of
> zoom levels and once we get out to whole earth or continent level the
> performance is poor. Our assumption is that it is the shrinking of the
> images which where is the time if being used up.
>
> The raster files are tifs with external world files, adding overviews
> helps a little.
>
> The zoom levels and output resolution can be fixed so if the overviews
> match exactly the required image size that look like it would work but
> we cannot see how to do this.
>
> So any advice on what are the most efficient file formats to open and
> the most efficient output format.
>
> The application is written in php mapscript which runs as a service
> and not via a browser.
>
> Thanks
>
> Ian
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I set the clouds in motion - turn up | Frank Warmerdam, warmer...@pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam and watch
the world go round - Rush | Geospatial Software Developer
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