Gabriel Roldán created GEOS-5078:
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Summary: Saved GeoServer tile layer gridsubset extents can overlap
the gridset's area of validity instead of being contained
Key: GEOS-5078
URL: https://jira.codehaus.org/browse/GEOS-5078
Project: GeoServer
Issue Type: Bug
Components: GWC
Affects Versions: 2.2-beta1
Reporter: Gabriel Roldán
Assignee: Gabriel Roldán
Fix For: 2.2-beta2
GWC (for some strange reason) uses an equality threshold when comparing
bounding boxes of just 0.03.
GeoServerTileLayer computes gridsubset extents by reprojecting the layer's
native bounds to the gridsubset's target CRS.
Due to the bounding box equality threshold, a reprojection inaccuracy may not
be detected, and the resulting gridsubset extent may overlap the GridSet's area
of validity instead of being contained in it. Hence the gridsubset's extent is
saved with aov overlapping coordinates.
This, later on, can produce the computed tile grid coverage to extend beyond
the full gridset coverage, and cause reprojection errors when asking GeoServer
for a metatile, depending on the data source.
Such is the case in 2.2-beta1 with the Arc_Sample coverage. It covers the whole
world in EPSG:4326.
When the bounds for the EPSG:900913 gridsubset are calculated, a small error
results from the reprojection, and gwc's BoundingBox.contains method doesn't
realize it, saving the gridsubset with wrong bounds.
When asking for a metatile, the gridset coverage for level 0 is -1 instead of 0
on the y axis, and the WMS fails to render the image.
So, in summary, make sure not to save gridsubset extents that are not contained
in the CRS area of validity, both for accuracy and to account for data sources
that fail when reprojecting outside the crs area of validity.
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