[Gdal-dev] Read-Only HFA dataset and overview creation

[Daniel]

Hello Folks,

 If i open an Erdas .img file in read-only mode i can't create any
 overviews. The .ovr overview support was removed from the HFA driver a
 while ago and before that a .ovr file was created when a .img file
 was opened as read-only but no i just get "BuildOverviews() not
 supported for this dataset"

 HFADataset::IBuildOverviews calls GDALDataset::IBuildOverviews if
 opened as read-only but that does not work anymore since the
 initialization of the ovrManager was removed (Changeset 8358)

 if( GetAccess() == GA_ReadOnly )
         return GDALDataset::IBuildOverviews(

I think that .ovr support for .img files would be good to have since
the .rrd style overviews modifies the original file. Another problem
with the .rrd files is Ticket #1109 (Building overviews on an
Imagine-created HFA file results in a segfault) which seems a bit
tricky to fix.

Previously i always opened files as read-only since i don't need write
support ATM but this is not possible any more.

Best Regards,
  Daniel Bäck