Wow!… GPSFix just alerted me to a new feature being beta-tested by Garmin on their latest handheld devices. You first grab a trail map or aerial photo as a jpeg - then overlay it on Google Earth as an image overlay - so that you can geo-reference it. Then you save as a kmz file - and drop it on your Garmin Oregon, Dakota or Colorado.
I’ve known about a hack to convert raster maps into psuedo vector files that can be viewed on a Garmin for some time - but this looks like a much better solution.
The original article is posted on the Garmin software update blog, and also refers you to their developer forums for more discussion.
Update1 from GPSFix based on a tip from Garmin: Keep each JPEG <1 megapixel (1024x1024), otherwise the device will need to reduce it’s resolution on the fly - which isn’t a good idea. Each image must also be under 3Mb in size. If you need to cover a larger area - you can use multiple images in the same kmz file (up to a limit of 100 image files on one GPS).
Update2: It looks like MapTiler might be a great tool for converting map files from one format to the Garmin custom kmz, along with the ability to break larger images into smaller tiles. The export feature isn’t coded yet, but there is discussion on Garmin’s forum suggesting that we all vote for it.