I have complete set of 1:50000 maps of Sri Lanka in .tiff format. They have .TFW files accompanied with them. Now I need to create maps to use with my etrex 20 device using those tiff files. How can I do it?
Garmin Products require JPEG format
You Can use Google Earth to Create Custom Maps for Garmin
"Garmin Custom Maps require your map be saved in JPEG format. If your map is printed, scan the map at an appropriate resolution¹, and save the image as a JPEG. If your map is electronic, such as a PDF, it may require conversion using GIMP or another suitable program to save it as a JPEG."
I posted a python script to use from ArcGIS here:
The different models support different numbers of tiles. You have to look at this limitation, the extent of imagery you want to use, and the minimum resolution you want to use. Then you need to possibly create multiple files from your original imagery, process each section of imagery with the script tool, and transfer the files from a laptop to the GPS as you need them (Garmin only support 1 "Custom Map" at a time). Many of the *map models only support 100 1024x1024 tiles. The Colorado and Montana support more. I experimented with changing the tile size to 2048 x 2048 and that seemed to still work and allow for quite a bit more data at a time.