Astrolabe is an embeddable library for placing icons on the Minimap, and on World Maps. Icons that are placed on the Minimap using Astrolabe are placed in a special buffer and their positions are continuously updated for player movement, based on the world map coordinates provided when the icon was initially placed. Icons remain in this buffer until they are removed.
Astrolabe also provides functions to compute the in-game distance between two points and translate a point from one zoom level of the map another.
For full documentation, see: http://wiki.esamynn.org/Astrolabe