Printing the Sky My Radio Forgot to Keep

Three printed curves on the shelf now. Coffee. No particular deadline except the kind you invent for yourself.

My hobby is collecting hobbies, and hobby number fourteen is APRS Skytrace Sculptures—mounting a tiny tracker on a foam RC wing, flying a deliberate pattern, then scripting the GPS points into a smooth 3D curve and printing a desk sculpture that captures the flight path in a single line.

The tracker speaks AX.25 packets to digipeaters I’ve never met, and those digipeaters gossip to IGates, and somewhere a map in Japan shows a foam aircraft drawing loops over frozen Alberta. I find this delightful. I also find it slightly absurd, which is probably why I keep doing it.

Fourteen hobbies in, and a thread is getting hard to ignore. When I carved a terrain tile in VFR Track Relief Printing, I was flattening geography onto plastic—a flight rendered as a ribbon across hills. When I measured the antenna yesterday in Antenna Lobe Lanterns, I was flattening signal strength onto a sphere and printing it as a glowing shell. Now I’m holding the flight itself, no terrain underneath, just the path floating in space like a wire bent by intention and wind.

Each version strips something away. The terrain tile had ground truth to anchor it. The lantern had a bearing reference—zero degrees is always north. The skytrace sculpture has neither. It’s just a line, suspended, claiming nothing except I was here, then here, then here.

The technical wrinkle I keep coming back to: APRS packets are not evenly spaced. The tracker beacons when it wants to, maybe every thirty seconds, maybe sooner if it decides speed or course changed enough to matter. So the raw data is a scatter of timestamps with no rhythm. The spline I fit through them is an interpolation—educated guessing about where the aircraft probably was between packets. Smooth enough to honour the air, not smooth enough to lie. That’s the line I’m trying to walk, and I don’t always get it right.

The sculptures sit on the shelf now. One is a simple loop, the shape you fly when you’re testing whether the system works at all. One is a figure-eight, ambitious and slightly off-centre because the wind was not my friend. One is the letter S—my initial, or an attempt at it—wobblier than I want to admit.

They don’t move. They don’t light up. They’re just lines in plastic, evidence that something flew a path and a computer agreed to remember it.

I keep turning the S in my hand, looking for the moment where I corrected too late, the gust I didn’t anticipate. The wobble is visible. The hesitation is visible. The sculpture is a flight recorder and a confession at once.

Fourteen hobbies. I’m still making things I can hold from things I can’t see. That doesn’t seem likely to stop.