Howto | Create Nagios Status Map Icons16 Sep 2010
Install GD Tools
$ sudo apt-get install libgd-tools
Create image in Gimp
Create a suitable image in Gimp, ensuring that it has a transparent rather than a white background.
From the menu - Image → Mode → Indexed and “Generate Optimum Palette” with “Maximum number of colours: 255”.
Save result as a PNG file, e.g. “router.png”
Convert to GD2
$ pngtogd2 router.png router.gd2 0 1