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A software thing I built: GPS on a 25MHz 486-SX

2026-09-16 | original

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Why This Matters

This is a nostalgic engineering anecdote illustrating how clever algorithmic choices—using integer-based Voronoi cell math instead of floating-point trig—enabled real-time GPS mapping on extremely limited 1990s hardware. It's a reminder of the resourcefulness required before GPS became a ubiquitous, taken-for-granted feature in modern devices, and highlights how IP and business fragility can cause promising innovations to vanish.

Key Takeaways

A 25MHz 486-SX without a math co-processor could run real-time GPS mapping thanks to an integer-based math library (Hipparchus) instead of costly floating-point trig calculations.
The story underscores how early GPS/GIS software required creative engineering workarounds that are now invisible thanks to modern hardware abundance.
Business and IP complications meant the developer lost access to the technology, illustrating how promising innovations can be lost when companies fail or contractors don't own their work.

Worth a Look

Garmin GPSMAP 66i Handheld GPS — This story is a great reminder of how far dedicated GPS hardware has come since 486-SX days. The GPSMAP 66i is a modern standalone unit that carries on that same tradition of purpose-built, rugged navigation devices, now with satellite communication built in. It's a fun way to appreciate the leap from Voronoi-cell math tricks to instant, precise positioning.

See Garmin GPSMAP 66i Handheld GPS on Amazon → Affiliate link — we may earn a commission on purchases, at no extra cost to you. Product picked by AI based on this article; it is not a tested recommendation.

I don't know if anybody cares about stuff like this, but I thought I'd share a quick story about a project I was hired to build back in the 90's as an embedded systems software developer. This is a project I wish I still had access to.

It's something I worked on where I was asked to build a "real-time GPS-driven moving map display" -- what we simply call a "GPS" today. Only today it's built into virtually every cellphone and tablet computer in the world.

I was asked to write this software so it ran on a hardware platform with a 25MHz 486-SX CPU, 32MB of RAM and the software would be in ROM. IIRC, the screen display was 1024x768. They gave me a laptop configured like that for testing. The 486-SX was the one without a math co-processor.

At the time, all of the math stuff I could find for GIS applications was built around heavy use of floating-point numbers and lots of trig formulas. (My BS was in Math/Computer Science.)

As it happened, a few months before that, an article was published in Dr. Dobb's Journal about a library that took a very different approach. It was called Hipparchus from a company named Geodesy. It used Voronoi Cells and reduced most math to 8- and 16-bit integer calculations with one or two single-precision floating-point calculations. It actually had higher resolution than Extended-precision floating point math!

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Explore topics: 486-sx cpu gps mapping hipparchus library voronoi cells dr. dobb's journal