Mr. Locator

Calculates the Maidenhead locator system geocode (AKA QTH locator or IARU locator) from the GPS position.

This locator system is used especially by radio amateur operators. It's similar to the GPS coordinates. Its advantage is that it's hierarchical, so the more characters of the locator you transmit / receive the more precise location you get. For example the locator for the Greenwich UK is JO01al18. If you hand over only the JO code, the other party will know that the target is located somewhere in the 20° x 10° square, for the JO01, it's 2° x 1° square, for the JO01al it's 5' x 2.5' square and for the JO01al18 it's 0.5' x 0.25' square.

Usually for the HF (high frequency) communication, just the 4 characters codes are used (e.g. JO01), because such precision is enough for the purpose. For the VHF/UHF (very high frequency / ultra high frequency) the 6 characters codes are usually used (e.g. JO01al). The last two characters are mostly written in the lowercase for better readability.

Wiki definition: https://en.wikipedia.org/wiki/Maidenhead_Locator_System
Source code: https://github.com/yarda/mrlocator