Add invocation for "what trail mile am I at?" about mouse

[mileswwatkins]

• GPX data: https://pctmap.net/gps/
• POIs: https://pctmap.net/trail-notes/

This GitHub repo already has GeoJSONs, but they're old: https://github.com/bwainstock/halfmile-geojson

[mileswwatkins]

Will expose this invocation:

mileage {trail} {requires Garmin location URL}

eg:

> mileage pct  - MouseUser inreachlink/ABC1234

The closest mile marker is 482

Will require:

• mile or half-mile coordinates (to 5 points of decimal-degree precision) for all trails
• utility to identify nearest point (using @turf/nearest-point)

[mileswwatkins]

I have a working PR for this (at least as far as the PCT), but have run into some major hurdles. Notably, different sources/guidebooks/shapefiles and different years of data use different mileages, both for the AT and the PCT; there's no canonical mileage open-data files AFAICT.

The PCTA website (using the NPS(?) ArcGIS Server) has a line that measures about 2498 miles and half-mile point data that counts 2661 miles(!!). But the PCTA's data book says that the total trail distance is 2450 miles. Most people (who'd be potential users of a paid Mouse service) will be using FarOut/Guthook which abides by the 2450 miles. There's no obvious open-data source for that, as far as I can find, so I cannot recreate mile markers. I anticipate that the AT would suffer the same data issues, from my early investigations into their data (eg, this message on their ArcGIS Server: Referecne Points at .5 mile interval. Not intended to be use for navigation. Distances come from GIS data not guide books or other navigation APPs.).

All that said, I should really be focusing less on this feature and more on the core competency of Mouse: real-time data updates. Rough navigation tools like mileage seem unnecessary. I'm going to close my WIP PR right now, but can revive it later if I want to use its geodata processing in another context.

[mileswwatkins]

wontfix