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January 2007
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2007.01.17 21:18 "Re: Elevation Data", by Frank Warmerdam
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