Comment by jacobolus
1 hour ago
You know what also works to get the Karney formula into a program? You can download Charles Karney's free software (MIT license) implementation in several [1] programming languages and then just make a library call – the API is straightforward. If you have comments or questions you can read his several clearly written papers describing the problem, its history, and his algorithm, or you can directly email him: he's a very nice guy, and pretty responsive.
[1] https://geographiclib.sourceforge.io/doc/library.html#langua...
Right, it was really more as a test of how much was contained in the training data set. For my purposes Vincenty is quite accurate enough. This isn't for millimeter level precision land surveying or measurements, but for distance in meters between microwave or millimeter wave band radio sites, point to point links. Even a distance difference of 4 meters plus or minus on a 12 km, 11 GHz band link is going to have no appreciable difference on link budget/reliability calculations, it can be that crude. But not so crude that I just want to throw Haversine at it when Vincenty exists and is not computationally expensive.
As this was for a test of "what happens if..." I also watched to see if it did any web searches or external data retrieval to build the test script, and it didn't.
I intentionally didn't give the LLM a direct copy of the software or a link to it, to see what it would do. In my case it was a randomly chosen example I could come up with in 10 seconds of imagination to see "hey what if I ask it to do this...". It also implemented a perfectly usable parabolic millimeter wave antenna gain efficiency calculator based on variable surface smoothness parameters, which is a lot more basic math.
As an aside: I'm quite convinced that an extremely precise version can be implemented that is significantly faster than Karney's, roughly comparable in speed to simpler naïve approximations. But for most purposes where the precision matters Karney's implementation is not any kind of bottleneck, so it's not clear it's worth spending significant effort on trying to do better.
Maybe that's something one of the big LLM companies might want to throw their machines at optimizing if they need to do a lot of geographical calculations.
One of the places where Karney does become computationally expensive (though still not ridiculous) is a scenario like this, working from a local in-RAM mariadb database that is a copy of the entire FCC radio license database:
Draw a 400x400 km size bounding box on a map
Find all FDD band plan (high/low split) microwave radio sites in that bounding box
Find those sites which have azimuth aim column data which indicates that they are aimed at each other (corresponding halves of a point to point link).
Do Vincenty (or Karney) calculation for distance and azimuth between all of them , treating the existing FCC column data for azimuth as suspicious (because it's hand entered by humans) to verify that each independent database rows for each site are actually corresponding halves of a PTP link.
Use various other logic to group the successfully matched halves of links together as points A and B of PTP links, and write them out to a geojson file with placemarks and line drawn between them.
Multiplied by the number of links that exist in an area like a 400x400km box drawn with Dallas, TX as the center, it's a lot to run through Karney. Actually does result in a lot of CPU load from combined db query due to the size of the db, and Karney calculation. But as I said, Karney isn't necessary, so it's instead implemented as Vincenty.