On Wed, 27 Apr 2005 12:23:33 -0400
Frank Warmerdam <fwarmerdam@gmail.com> wrote:
Folks,
First, this is a warning that GDAL CVS will likely be somewhat
unstable for a couple weeks. I am starting to commit substantial
changes to provide Persistant Auxilary Metadata to many formats,
including read-only formats.Persistent Auxilary Metadata is basically intended as a way of
associating an extra header file with files that can store various
information that isn't supported by the format itself. That is
auxilary metadata like coordinate systems, geotransforms, histograms,
generic metadata, color tables, and so forth.The auxilary metadata is stored in a .pam XML file. The .pam filename
is the original dataset name plus .pam. So the pam file for utm.jpg
would be utm.jpg.pam.The general idea is to ensure we can associate a variety of auxilary
information (and cache statistics) for most GDAL supported formats,
whether they have support for such structures in the format itself or
not.The XML structure is similar to how such information was stored in
.vrt files, for those familiar with vrt.The process to PAM enable a driver is to derive it from GDALPamDataset
and GDALPamRasterBand instead of GDALDataset and GDALRasterBand
and then to make a few minor adjustments in the driver. It is my
intention to apply this change to almost all the drivers.In the meantime, if you update from CVS please also do a clean
rebuild.I plan to write up a tutorial document describing how PAM works
fairly soon.
I think GRASS maps could benefit from this as well. Good|some|any
meta-data support has long been missing in GRASS and this might be
the answer. Synergy & other buzz words plus. Looking forward to
further information on the implementation.
Hamish