[mapserver-users] raster query strategy

[Frank Warmerdam]

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.

Best regards,

> On 08/17/10 16:09, Richard Greenwood wrote:
>> I am working with a single band raster of 10mX10m cells. I have added
>> overlays with gdaladdo and it displays nicely.
>>
>> When I query the layer I am using MODE=nquery, not MODE=query. The
>> reason that I am using nquery is unrelated to the raster layer, but
>> I'm pretty much restricted to using that mode. At large scales this
>> returns at least 2 cells, which I can average easily with JavaScript
>> in the browser. However at small scales I'm getting 10s of 1000s of
>> cells which are really slowing things down. It does not appear that
>> query or nquery mode is using the overlays. Anyone disagree with that
>> assumption?
>>
>> So the only solution that I've come up with thus far is to resample
>> the raster to larger cell sizes and use the min/max scale denominator
>> to select a layer with cell size appropriate to the scale. Anybody
>> have other ideas?
>>
>> Thanks,
>> Rich
>>
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