Implement a sensible no-data strategy for ArcSDE rasters
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Key: GEOT-2413
URL: http://jira.codehaus.org/browse/GEOT-2413
Project: GeoTools
Issue Type: Improvement
Components: data arcsde
Affects Versions: 2.5.4
Reporter: Gabriel Roldán
Assignee: Gabriel Roldán
ArcSDE rasters no-data samples are bitmasked. This means an extra bitwise mask
exist for each raster band, so for geophysics coverages it is not like we can
just create an extra band acting as a no-data mask, since each band may have
no-data samples at different locations.
The strategy would be to "promote" a raster sample type to a higher one on the
fly, in order to make room for an extra value set as the no-data one.
This would be completely cool since there's no obligation that the run-time
sample representation matches the storage one, so we can promote 1 and 4 bit
bands to 8 bit and assign, for example 255 as the no-data value, keeping 1 and
2 the "data values" for 1-bit rasters, for example.
Some research done in that respect suggests the best place where to introduce
this promotion is at the lower level one. That is, on TileReader, given the
knowledge of the internal structure needed to perform the promotion and to keep
the ImageInputStream implementation as decoupled from these details as possible.
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