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On 08/18/10 00:46, Richard Greenwood wrote:
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cite="mid:AANLkTikHiiXDyHSG2yNUe1KA4J2qLk5A7PgjQsN_xw6i@mail.gmail.com"
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<pre wrap="">On Tue, Aug 17, 2010 at 2:57 PM, Frank Warmerdam <a class="moz-txt-link-rfc2396E" href="mailto:warmerdam@pobox.com"><warmerdam@pobox.com></a> wrote:
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<pre wrap="">Jan Hartmann wrote:
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Is this a bug? Shouldn't MapServer use the gdaladdo overviews at the
appropriate scales?
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<pre wrap="">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.
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<pre wrap="">
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. </pre>
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<font face="Times New Roman, Times, serif">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?<br>
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Jan<br>
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