On 08/18/10 00:46, Richard Greenwood wrote:
On Tue, Aug 17, 2010 at 2:57 PM, Frank Warmerdam<[email protected]> wrote:
Jan Hartmann wrote:
Is this a bug? Shouldn't MapServer use the gdaladdo overviews at the
appropriate scales?
Rich / Jan,
No, generally I treat raster query as an "exact" operation done
against the full resolution data. The overviews are only used
to satisfy downsampled RasterIO requests such as drawing a reduced
resolution map.
I wouldn't classify it as a bug, but it is an interesting question.
Displaying a map at 1:1,000,000 the user clicks and gets 30,000 cells
from my 10m grid. Which one is right, or "exact"? Right now I'm
averaging them, which is pretty much what gdaladdo has already done.
If you click on a raster map and want to know the value of the area
under that click, shouldn't that be the value of the pixel in the
original resolution, just as Frank implemented it in GDAL? What you are
doing now is essentially querying a square, with an area varying
according to scale, and there is no other way to do that than by
generalizing. Nothing wrong with that, of course, but is that really
what you intend? And if MapServer's query function forces you to use
that option, isn't *that* a bug?
Jan
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