Quickstart

gentile.py is a quick hack that will convert a jpeg of a map into tiles that Garmin GPS units can display instead of the regular basemap.

run it like this:

gentile.py -t 30 -i North-Shore_49.470808_49.336874_-122.980824_-123.131780.jpg   

and it will split it into 1024x1024 pixel geo-anchored jpegs, all wrapped in one kmz file:

North-Shore.kmz

Plug in your GPS via USB and copy the kmz files to its /Garmin/CustomMaps/ directory. These map tiles should now be displayed on your GPS when you look at that area.

System Requirements

• python 2.7
• imagemagick convert & identify programs (or graphicsmagick variants)
• zip

Tested on OS X 10.10 using brew to install imagemagick.

Map File Names

Maps can be jpeg, tiff or other formats supported by ImageMagick. The file name of your map must include its bounding box (lat/long) in decimal degrees. The syntax is:

North-Shore_49.470808_49.336874_-122.980824_-123.131780.jpg   

<name>_<north-lattitude>_<south_lattitude>_<east-longitude>_<west_longitude>[.type]

Don't use underscore anywhere in the name except as one of the four separators above.

Figuring Out The Bounding Box

Try using GoogleEarth to load an image (Add->Image Overlay) and fiddling with the coordinates in the Location tab to postion the map. Then try those coordinates with gentile.py. Tune it by using the GPS with the kmz files and observe if it is offset N-S and/or E-W. Regenerate the tiles with adjusted coordinates.

How Many Tiles

The '-t' parameter suggests the maximum number of tiles to generate. Setting it too low may make for grainy tile images because gentile.py will reduce the resolution of (a copy of) the image until it can be cut it into ~maxtiles 1024x1024 pieces.

Setting maxtiles too high may exceed the capacity of your GPS device. A Garmin 62s can hold a maxiumum of 100 tiles while some other models support 500.

Run the following for other options:

gentile.py -h