Hm. Good point. I wasn't involved in the sourcing of the data, and don't really know what it represented. The description I was given, as best I remember it, was that the points represented scintillations on the memrane that forms the cell walls of an amoeba-like thing. The creature can stretch bits of itself out into limb-like appendages, much like you see here.

The problem is that being 3 dimensional, you get scinitallations from all over the outer membrane, not just around the 2D edges. So reconstructing a top-down, 2D representation of the thing, required connecting the dots that formed the outer edge of it, whilst ignoring those that came from the top of it. If you plot the points, your eyes/brain allow you to "see" the outline, and people would spend hours manually tracing the outines in GDDM so that they could extract the creatures image from the background before processing it further.

Effectively it was an "edge tracing algorithm", but as the entire image was constructed of dots, and the background had plenty of them also, it was rather more complex. First you had to low-pass filter the points to exclude noise and as much of the background as possible without lossing too much definition in the creature. then attempt to draw a single line around the thing. As the points were digital on a defined grid, you end up with a complex polygon.

Maybe that "single line" is the extra qualification you are after?