A developer has turned the rail network into an accidental camera, one track mile at a time.
The project, called Linecam and published at philo.gay/linecam, points a camera out a train window and grabs a single narrow slice of the passing scenery over and over as the train rolls forward. Because the train moves at a steady pace along a fixed line, those slices stitch together into one unbroken image, the same way a flatbed scanner's sensor head crawls across a sheet of paper to build a picture line by line. Instead of a document, the subject is whatever track and countryside the train happens to pass. The post picked up 66 points and 12 comments on Hacker News, a solid showing for a project that is really just an old imaging trick applied somewhere nobody expected it.
The technique itself, known as line-scan or pushbroom imaging, is not new - it is how satellites and aerial mapping planes have captured long strips of terrain for decades. What is interesting here is the reframe: a commuter rail network already provides the steady, predictable motion that pushbroom imaging needs, for free, without any custom hardware beyond a camera and a window seat.
It is the same principle as a scanner you might have sitting under your desk, just swapping a moving sensor for several tons of steel and a timetable.