Various overview selection algorithm issues in AbstractGridCoverage2DReader
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Key: GEOT-1643
URL: http://jira.codehaus.org/browse/GEOT-1643
Project: GeoTools
Issue Type: Improvement
Components: core coverage
Affects Versions: 2.5-M0, 2.4-RC0
Reporter: Andrea Aime
Assignee: Simone Giannecchini
Fix For: 2.4.0, 2.5-M1
The overview selection algorithm in AbstractGridCoverage2DReader.setReadParams
suffers from various issues:
* it assumes overviews are ordered from coarser to more fine grained, with
subsequent gdaladdo calls it's possible to get a different order (for example,
in one of my tests by mistake I got this "Band 1 Block=256x256 Type=Byte,
ColorInterp=Red, Overviews: 1688x1500, 844x750, 422x375, 211x188, 3375x3000"
* it selects the "overview with the highest lower resolution compared to the
requested one, this ensure more speed but less quality". Well, no wonder people
are complaining GeoServer does not work with hires images, to have it use the
native resolution one has to exceeed it in the getmap request. The lowest among
the higher resolutions should be used instead. If the overviews are quite far
away the result is disastrous... for example, in one of my tests I skipped the
level 2 to save space, and in fact I did get quite ugly looking results (that
is, I run gdaladdo file.tiff 4 8 16 32)
* the code assumes a comparison on just one axis is ok, but in reality the
overview resolution might be lower on the y axis whilst the request has the
opposite situation. Both should be taken into consideration
Simone, I can cook a patch for all of the above. I feel strongly against the
"fast but inaccuarate" option above, but maybe we can keep it by adding a
rendering hint of sorts? The AbstractGridCoverage2DReader could have a field to
allow that choice, and the subclasses could use a hint to allow for that choice
(it is possible to set a JAI wide hint?)
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