(a) Simple turbulence crossing (t = 494, α = 85°). (b) Boundary of magnetic structure with strong shear, but no reconnection (t = 247, α = 33°). (a) and (b) structures have been selected via the threshold on J only (true negatives). (c) Crossing of a reconnection separatrix (t = 494, α = 85°), selected via the threshold on J and on the scale-integrated PVI, as well as using human labeling (true positive). See text for further details. (d–f) Overview of the structures crossed in the 2D box.