Dan Greve wrote:
Greetings,
I am currently accessing datasets which are embedded inside a single
file. Each dataset is a given file offset and length inside of the
larger file.
I saw in the latest doxy-docs here
<http://www.gdal.org/ogr/cpl__vsi_8h.html> that there is a
VSIInstallSubFileHandler for doing just that, and look forward to
testing it out. My concern with it, as well as the normal
VSIMemFileHandler, is in accessing large files. I have 2 GB images,
embedded within files that are up to 100 GB in size. Does the
VSIMemFileHandler do any sort of paging so that the entire source image
is not read into memory?
Dan,
The VSIMemFileHandler treats a memory buffer as a file. There is no support
in it for paging from a file so it is only suitable when you are prepared
to load the object into RAM.
The VSISubFileHandler on the other hand just manages access to a file through
regular file access handle, but keeping track of an offset to the sub file.
So it does not use appreciably more memory than a normal file access.
I believe the subfilehandler would be the suitable tool for you. I believe it
is only available in GDAL trunk, not 1.6.x.
Best regards,
--
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up | Frank Warmerdam, [email protected]
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush | Geospatial Programmer for Rent
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