[gdal-dev] MrSID mask band support

[Frank Warmerdam]

On 11-02-14 03:52 PM, Brian Claywell wrote:
> I'm attempting to use CreateMaskBand() on a MrSID dataset with GDAL
> 1.8.0 and receiving the error that "CreateMaskBand() is not supported
> on this dataset." I presume this is because mask band support was
> implemented using the GDALDefaultOverviews manager, and since MrSID is
> a multi-resolution format, the overview manager is never initialized.

Brian,

This is a lucid deduction.  I believe you are right.

> Is there a way to make mask bands work with MrSID datasets out of the
> box? Barring that, since the MrSID driver reimplements the
> overview-related virtual functions to bypass the default overview
> manager, would there be any harm in initializing the overview manager
> when a MrSIDDataset object is created?

The one caveat I might offer is that it would be prudent to have
MrSIDDataset override IBuildOverviews() or else people will find they
can build external overviews for MrSID but they will never be used.
The IBuildOverviews() override would presumably just report that
overviews are "built in" for mrsid and building them is unnecessary.

If you try this out, I'd be interested in a patch submitted via Trac.

A similar approach would likely apply to formats like ECW and JPEG2000
with built in overviews, but where masks would still be useful.

Best regards,
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