[Gdal-dev] GDAL CVS Instability - Persistant Auxilary Metadata

Frank Warmerdam fwarmerdam at gmail.com
Wed Apr 27 12:23:33 EDT 2005


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 

I plan to write up a tutorial document describing how PAM works 
fairly soon. 

Best regards,
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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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