NOTE: This is a work in progress.  CVS sources may or may not 
function properly (or even compile) at any given point in time.


About imgdecode
---------------

This program is designed to aid in the decoding of Garmin IMG files.
It hexdumps the IMG file side-by-side with plain-text descriptions
of what the particular bytes in the file represent.  Unknown
data blocks are either unlabeled or labeled with a ???.  Files are
created in a directory named after the IMG file, with separate files
for each subfile & section.  Naming convention is:

   offsetbegin-offsetend.subfile.section

For example:

   00130348/
	00000001-000018bf.DSKIMG.header
	00001a00-00001a1c.RGN.header
	00001a7d-00002449.RGN.level.02
	00002548-00003d99.RGN.level.01
	00003ee2-0003a972.RGN.level.00
	0003d200-0003d2bb.TRE.header
	0003d2bc-0003d30f.TRE.mapinfo
	0003d310-0003d315.TRE.copyright
	0003d316-0003e0a1.TRE.subdivs
	0003e0a2-0003e0b1.TRE.levels
	0003e0b2-0003e0cc.TRE.polylines
	0003e0cd-0003e0f3.TRE.polygons
	0003e0f4-0003e1a4.TRE.points
	0003e1a5-0003e298.TRE.unknown1
	0003e299-0003e29d.TRE.unknown2
	0003e400-0003e515.LBL.header
	0003e516-0003e51e.LBL.sort
	0003e51f-00047ddd.LBL.labels
	00047dde-00047de0.LBL.countries
	00047de1-00047de5.LBL.regions
	00047de6-00047e30.LBL.cities
	00047e31-00047e60.LBL.zipcodes
	00047e61-00048d50.LBL.unknown1
	00048d51-0004c930.LBL.poi_properties
	0004c931-0004c94c.LBL.unknown2

As you can see, it generates a LOT of output.  Be prepared.

Note that I am not doing detailed bitstream parsing for polylines
and polygons at the moment.  Mostly this is to get past those things
that are already known and on to sections (like NET and NOD) that
are unknown.  I calculate the number of points in the -line or -gon
but probably will NOT add the coords themselves in order to keep
the output to manageable levels (it's currently at 20x the IMG file).

What you also see is the beginning of a general-purpose library for
interacting with IMG files (including the "combined" map files
generated by MapSource and MapSend when uploading a map set to the
GPS or a card writer).  Because the decoder needs raw access to the
IMG data, many of the functions that would normally be methods in
the various subfile objects (tre, lbl, rgn, etc.) are implemented
in the decoder itself, but as the library develops this code will
get duplicated into the objects.


What isn't working
------------------

NOD section "unknown2" is not correct.  There are offsets into this
file from NET and I know where they are, but don't understand the
algorithm for getting to them, so parsing NOD is pretty much impossible
for now.

Much of NET is still unknown.

This still blows up on some IMG files and I'm not sure why.  If you
are running against a CityNav or City Select NA product, I can look into
it if you send me the file name (and product version).