Read the wiki page on it, run through the psuedocode on pen and paper a few times and then implement it. Source: I did this when I wrote a library for reverse

Read the wiki page on it, run through the psuedocode on pen and paper a few times and then implement it. Source: I did this when I wrote a library for reverse geocoding which uses a kd tree. https://github.com/AReallyGoodName/OfflineReverseGeocode https://github.com/AReallyGoodName/OfflineReverseGeocode