[gdal-dev] Get a rough overview image via RasterIO

[Frank Warmerdam]

Oliver Eichler wrote:
> Hi,
> 
> zooming out of a raster map is always a very resource hungry task as a large 
> area of points have to be read and reduced to the viewport size. 
> 
> For a steady map RasterIO does the perfect job. However if the user zooms out 
> of a map very fast via mouse wheel RasterIO eats up too much time to allow a 
> smooth zoom. 
> 
> Thus my question: Is there a way in GDAL to get a quick overview picture for 
> smooth zooming.

Oliver,

Generally speaking you can't read data from GDAL and display it fast enough
to provide smooth zooming.  The usual approach is to preload raster data into
textures and then re-render those frequently for fast, smooth zoom.  This
is what OpenEV does.  And it just reloads the textures from more appropriate
resolution levels when things don't seem busy.

Best regards,
-- 
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