[mapserver-users] Raster image performance

[Ian Walberg]

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: fwarmerdam at gmail.com [mailto:fwarmerdam at gmail.com] On Behalf Of Frank Warmerdam
Sent: Friday, November 11, 2011 11:52 AM
To: Ian Walberg
Cc: mapserver-users at 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 <ian.walberg at airborne.aero> 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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>



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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com light and sound - activate the windows | http://pobox.com/~warmerdam and watch the world go round - Rush    | Geospatial Software Developer