[Gdal-dev] ArcGrid to IMG conversion: huge file

[Frank Warmerdam]

Markus Neteler wrote:
> Hi,
> 
> when converting the
>   Landscan Global Population 2000 Database
> from
>   http://www.fao.org/geonetwork/srv/en/metadata.show?id=1261
> 
> which is
>   504K    ./info
>   167M    ./pop2000
> big, a resulting IMG file becomes:
>   3.5G    pop2000.ige
>   8.0K    pop2000.img
> which is pretty much more (for free :-)
...
> Apparently the NoData isn't passed to IMG.
> Is the created IMG file probably uncompressed
> which leads to this big file size?

Markus,

Just yesterday I came to the realization that there is no "nodata"
support in the Erdas Imagine driver, and in fact, I have no idea how
nodata values are represented in .img (HFA).  If anyone has a modest
sized .img file with properly nodata values I would appreciate a
copy so I can investigate.

On the size issue, arc/info binary grids use various compression
techniques and it is clear that in this case they are quite effective.
By default imagine files are uncompressed.

You might want to try the COMPRESSED option for the HFA driver.  It
was contributed, and I haven't used it much, but it enables a simple
compression type in the imagine format.

eg.

gdal_translate -co COMPRESSED=YES in out

If the imagine driver determines an "ige spill file" is needed it
is possible that the compression will not work.  Let me know if
there are problems.  You might also test on a section of the file to
verify that compression does work for smaller datasets.

Best regards,
-- 
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