Show HN: Red Grid MGRS – Open-Source DAGR-Class GPS Navigator for iPhone (github.com)

2 points by redgridtactical 4mo ago ↗ HN

The military's DAGR GPS receiver costs $2,500 and weighs a pound. I built an open-source alternative that runs on your iPhone — live 10-digit MGRS coordinates, magnetic declination, waypoint navigation, 8 tactical tools, and 6 radio-ready report templates (SALUTE, 9-Line MEDEVAC, SPOT).

React Native / Expo, ~15k lines of JS, fully offline, zero tracking. Location data never leaves memory.

Free on the App Store with an optional $9.99 Pro upgrade. Would love feedback on the UX, the MGRS math, or anything else — still actively developing.

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redgridtactical 4mo ago ↗

I wrote the MGRS conversion from scratch using the DMA Technical Manual 8358.1 rather than pulling in a library. The trickiest part was handling the Norway/Svalbard UTM zone exceptions and getting the 100km square letter cycling right. Happy to walk through any of the math if anyone's curious.