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Date: Wed, 17 Jan 2007 16:18:21 -0500
From: Frank Warmerdam <warmerdam@pobox.com>
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To: Joris <joris.at.lebbeke@skynet.be>
Subject: Re: [Tiff] Elevation Data
References: <200701170225.l0H2PhRY014173@tux.cubewerx.com><Pine.SOC.4.60.0701162049080.13644@blade.simplesystems.org> <000701c73a0e$958b8390$70c9f451@dfgrrxsknr4e> <AA6DDFA4E046A24585BC828A78155B470146027D@US-MAIL.ingrnet.com> <001701c73a4f$e9e40250$22a94057@dfgrrxsknr4e> <Pine.SOC.4.60.0701171002580.13644@blade.simplesystems.org> <001d01c73a54$cf784ca0$22a94057@dfgrrxsknr4e> <45AE7300.1070909@pobox.com> <002e01c73a5d$05b29e30$22a94057@dfgrrxsknr4e>
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Status:   

Joris wrote:
> In my (prejudice, on-track and very limited) mind, large image handling
> is pipeline-based. If I need to render a large TIFF (or any TIFF for
> that matter), I set up a pipeline that decodes, resamples, and converts
> color and all. I next start pulling the pipeline, and as results come
> in, I progressively update display.
> 
> That's just one very typical example, of course, of what I regard
> 'progressive streaming' of imaging processes. But it's sufficient to
> explain the dynamic sampling is rather awkward in this situation. I'd
> have to set up a first pipeline that decodes and gathers range, and run
> the complete pipeline, before I'd be able to set up the second pipeline
> with the detected range in the color conversion steps. For huge images,
> that's many seconds before the second pipeline is even build, which
> conflicts with my need to start progressive build-up of display asap.

Joris,

OK, I see your point.  when I saw progressive streaming I wondered if
we had morphed into a talk about reading stream data from the net or
something.

For the record, I only *sample* the data to establish a range for
scaling.  I have an algoirthm that takes roughly the square root of the
number of tiles/strips, reads them and uses that as a presumed reasonable
range to scale.  This takes relatively little extra time even for very
large images.

Best regards,
-- 
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam@pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | President OSGeo, http://osgeo.org
