With IMGinfo you can inspect the contents of an IMG file (those on your GPS, but also the files used by MapSource) or (with limited info) a GMP file.
It also enables you to view the information in a TDB file (this means that the separate program TDBinfo is dropped).
There is an option to extract the contents of an IMG file (not that you can do much with it), and an option to view the bounds of the map segments on a map in your browser.
IMGinfo for the Mac is a 64-bit application.
No fancy installer, just extract the file and put the contents in a folder of your choice.
Using the GUI-version of JaVaWa MapConverter is the easiest way to convert maps from the old 'Registry' type to the .gmap type, but some might have a need to incorporate the map conversion in a workflow. Here you can download a command-line version:
New in 0.8: solved problem with relative paths.
New in 0.7: option to use configuration file with more customisation parameters.
New in 0.6: problem with accented characters in folder and file names resolved.
New in 0.5: removes 'dot underscore' files in macOS after conversion of maps with a non-Mac OS drive as destination.
New in 0.4: fixed bug not overwriting certain files when it should do so; fixed problem with ExFAT formatted drives.
New in 0.3: option to specify the name of the .gmap folder.
jmc_cli -src=source_folder [-dest=destination_folder] [-bmap=basemap.img] [-gmap=mapname.gmap] [-v]
jmc_cli -config=mapname.cfg [-v]
|-src||(Relative) path to folder with map files you want to convert|
|-dest||(Relative) path to folder where the .gmap folder will be created|
(optional; when omitted the parent folder of source_folder will be used)
|-bmap|| Name of .img file with overview map (optional)|
(Needed only when jmc_cli cannot decide which file to use)
|-gmap||Name of .gmap folder (optional; when omitted the map name will be used)|
|-v||Verbose output: display every step in the process (optional)|
|-config||Use parameters from config file; see included sample|
Use quotes around paths when they contain spaces, or (Mac/Linux only) escape the spaces with backslashes. (not in the config file!)
1: wrong parameters
2: missing files
3: error in processing files
4: unhandled exception
Linux users: this is a 32-bit application; it may be necessary to install the appropriate libraries when you use a 64-bit Linux version.
The map creator has to provide the TYP files and to change the batch file accordingly.
Included with this tool is the command line version of GMapTool. GMapTool is licensed under the Creative Commons Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0) License.
Garmin used to have a lot of documentation about their extensions on the gpx format on http://developer.garmin.com/schemas, but that was lost when they redesigned the developer site. A couple of days before the site was changed I copied that stuff with the idea that it might be removed some day.... Just in time, as it turned out.
Well, for those that need it for creating programs that read or write gpx or tcx files: here it is.
Tip: Garmin's programs are very strict regarding validness (but every program working with XML data should be), so make sure your gpx output is valid. You can create your own extensions, as long as you provide a reference to a schema that defines the extension.
Developer's Manual (pdf)