An offline Maidenhead grid converter

This post is an announcement, with about 2 hours and 11 minutes to spare (minus however long it takes to write!), of my project for OFFLFIRSOCH 2026. If you've emailed me in the past day and a half or so to let me know about your own project and you haven't heard back yet, please accept my apologies and rest assured I've seen your mail and your submission *will* be included in the round up! I haven't replied yet because I've needed every spare minute to get my own project finished this year due to having a bunch of other stuff on in March. I tried to compensate for this by keeping the project simpler than in earlier years, and yet, here we are...

In amateur radio circles, there's a system, known as the Maidenhead Locator System, for succinctly representing a location on the Earth's surface to a relatively decent accuracy (within a radius of approximately 10km) as a string of two letters between A and R, two digits, and another two letters between A and X. The city of Turku, for example, at 60.45°N, 22.27°E, can be represented by the string "KP10DK", which is substantially shorter and less fiddly than "60.45°N, 22.27°E", especially if you're trying to convey it by Morse code. The system is actually a little more flexible than this. When less accuracy is necessary, you can use just the first four characters, "KP10", and this is widely seen in digital modes often used on the HF bands like FT8 or WSPR. You can also get even greater accuracy by extending the system and adding another two digits.

Maidenhead Locator System at Wikipedia

For OFFLFIRSOCH this year, I've written a tool which converts back and forward between Maidenhead locators and latitude and longitude coordinates. To make it a slightly more viable replacement for an online converter (which will typically show you a marker on a world map when you give it a locator), when given a locator it will also provide an general region of the world (e.g. "Europe" or "South America" or "Central Asia"). If the $LATLON environment variable is defined (as it typically will be for regular users of either of my previous OFFLFIRSOCH projects, `city` or `day`), the tool will also tell you how many kilometres away a supplied locator is from your location. If $LATLON is defined and you don't provide any other inputs, it will tell you the Maidenhead representation of your own location.

It's written, like my other OFFLFIRSOCH projects, in Lua, and has no dependencies other than the standard library. There's no documentation yet, sadly, but I'll add it in the coming days, and it's not too hard to figure out anyway.

`maidenhead` source repository at Sourcehut